Some tweets from the Toro Rosso account after that breakdown for Gasly.

Kayleigh: Hahaha better get used to those engine issues, Pierre!

Pierre Gasly pulls off on to the side of the track in the stadium section. A terrible start for the Toro Rosso team today. There is smoke coming from the vent immediately behind where he is sitting.

"Engine problem," says Gasly, and that could well be his session done already.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Reuters

McLaren have taken engine penalties on both cars in Mexico in anticipation of it being a difficult weekend for their car. It’s ironic, then, that Fernando Alonso in particular looked especially strong on Friday, eighth and seventh fastest in the two sessions.

“We were surprisingly competitive, P8 and P7, on a circuit we did not expect so very good signs and very positive Friday,” he said.

Pity he and Stoffel Vandoorne are starting at the back, then. Of course the reality is that even with a good qualifying position the race would be difficult for McLaren.

Slow on the straights and with relatively poor hybrid performance, they would be a sitting duck for the cars that would likely have been close behind - the Force Indias, Williams and Renaults.

Allan McNish
BBC Radio 5 live sports extra Formula 1 analyst

It's very windy. The wind has picked up this morning and is pushing dust down the start and finish straight, we saw that cause a few spins yesterday.

The other thing is the altitude. The air is very thin which means that your downforce levels are significantly less and your cooling is much less. It's important to manage these things.

And the hour-long session is under way. Sebastian Vettel is one of the first to get out on the track.

It's a bit chilly today in Mexico City. We're expecting it to be much warmer come race time on Sunday so not too sure how representative this session is going to be.

Image source, .

Here's a key stat around Lewis Hamilton's success this year.

He's the only driver to complete all 999 laps of the season up to now - 107 more than title rival Sebastian Vettel.

That's consistency from the Mercedes team, but also a knack for staying out of trouble from the Briton.

Mark Gallagher
BBC Radio 5 live Formula 1 analyst

Red Bull look like the men to beat this weekend.

Mercedes look like they might have some grip issues, and then there's Vettel and Raikkonen in contention, so we should see six drivers and three teams going for it on Sunday.

BBC Radio 5 live sports extra

Image source, AFP/Getty

Here's how you can follow today's action on BBC Radio 5 live sports extra:

Third practice

5 live sports extra (and listen online) - 15:55 BST

Session starts - 16:00 BST

Qualifying

Live text commentary - 18:00 BST

5 live sports extra (and listen online) - 18:55 BST

Session starts - 19:00 BST

Listen along by pressing the play button at the top of this page.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Getty Images

Pierre Gasly and Brendon Hartley are poised to form the Toro Rosso driver line-up in Formula 1 in 2018.

Team boss Franz Tost said there was a "high possibility" the Frenchman and New Zealander would stay on next year after being drafted in late this season.

And the Austrian confirmed Russian Daniil Kvyat, who has raced in F1 for one of the Red Bull teams since 2014, had been dropped from their programme completely.

Gasly and Hartley have in total so far raced in only three grands prix.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Reuters

Red Bull team boss Christian Horner on Friday rather pointlessly repeated his desire to see a) F1 ditch hybrid engines next year; and b) return to a high-revving V12. Pointless? Because neither is going to happen.

This formula will stay until 2020. And plans for a new engine formula after that will be presented to the teams by F1 owners Liberty and governing body the FIA at a meeting on 31 October (Tuesday, when everyone is back in Europe).

It is likely to be based heavily on the current engines, in terms of being a small capacity turbo with heavy electrical elements. The question is what form of electrification? Because the stated aim of Liberty Media is to bring the costs down and close up the competition.

Will they ditch the MGU-H, the hybrid element that recovers energy from the turbo? If so, how to recuperate the 60% of electrical energy that will be lost?

Four-wheel drive, and including the front axle in energy recovery, appears not to be on the agenda because of cost, weight and complication.

Quite possibly it will be a single or twin turbo with much more energy recovery from the rear axle, which is said to be do-able. But everyone is keeping their cards close to their chests for now. One question remains unanswered - it’s hard to see how costs can be reduced by introducing a major engine re-design. Any change is going to cost significant money.

Speaking of Red Bull, Max Verstappen sounds happy with the performance of his car yesterday.

BBC Sport app users may need to click on the links to see the tweets.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Reuters

Red Bull looked very good on Friday. Daniel Ricciardo topped second practice and matched Lewis Hamilton for race pace - albeit doing only four laps on his race simulation run as opposed to 27 for the Mercedes.

And Max Verstappen was even faster than both, but doing only two laps of race running. Their restrictive running makes it difficult to read too much into Red Bull’s race pace, but Verstappen was convinced “we’ll be there” on Sunday.

Their problem is this afternoon. They are likely to be out-qualified by Mercedes and possibly at least one Ferrari because Renault lacks the qualifying power-boost mode of the two other teams.

And track position is going to be a major advantage in a likely one-stop race on a track where overtaking is difficult, despite the long straights.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, AFP/Getty

Seven days after a difficult Friday in Austin, the same happened in Mexico for Sebastian Vettel.

In the US, it was a spin and then a handling imbalance that disrupted the German. In Mexico, the fire extinguisher went off in the cockpit.

“Another Friday that didn’t go 100% right,” Vettel said. “We had a fire extinguisher let go. Initially it was just burning but it turned out to be very cold.

"I had to go back and we changed it and lost some time. Short track, lots of traffic on the long run. The car was a bit so-so.

"Some laps were good, others not - so the car in general is quick. We need to work a little bit. It is more about finding the balance and then we should make a good step forward.”

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Getty Images

For some weeks now, the impression coming out of Mercedes has been that Mexico would be a difficult weekend for the world champions.

The long straights suit them, but not so the high altitude, which requires all teams to run at maximum downforce - and Mercedes’ high downforce package is not as effective as those of Ferrari and Red Bull, as Monaco, Hungary and Singapore have proved.

So far, though, things are going well. Valtteri Bottas topped first practice and Lewis Hamilton came second in both, despite a spin at the Esses on his first run of his second session, and they look very much the team to beat.

“I come into these days with no expectation and we just have to focus on doing our job,” said the Finn.

“The car did not feel great this morning. I made some good changes and then had that big spin and destroyed that first set of tyres but fortunately recovered with not such a bad couple of laps on the ultra-soft going out and then I did a very long run - 27 laps.

"I think we are looking quite good. I think it is going to be close. I was expecting us potentially to be worse off here but it is looking quite good.”

His long run was stunning - the same lap time at the end as at the beginning. Mercedes look strong.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Getty Images

The jeopardy has gone out of the title fight, following Ferrari’s foot-shooting exercise in Asia. But as an individual grand prix, Mexico has many question marks hanging over it, underlining potentially just how much Ferrari have lost by their implosion.

Mercedes came to Mexico fearing the track and what it might mean for their competitiveness. So far, those fears seem to have been allayed, the team looking very quick on Friday.

But Red Bull were right with them and look set to prove strong competition in the race, if not in qualifying. Ferrari? Friday was less successful for them, but Sebastian Vettel still believes they will be fine once they have sorted themselves out overnight. This could be a three-way fight at the front.

And this was the final order for session two. Hamilton spun early in the session but was second quickest overall behind the Red Bull of Daniel Ricciardo.

Image source, .

Let's start off with a quick recap of what happened yesterday.

This is how it finished in the first practice session, with Valtteri Bottas, who has failed to make the podium in three successive races, the quickest man.

Image source, .

Welcome along to BBC Sport's live text commentary from day two of the Mexican Grand Prix weekend.

Third practice gets going at 16:00 BST and we will then have qualifying at 19:00 BST. It could be a dramatic day.