We've dipped below two hours left of the morning testing session.

Sergio Perez is leading the pack, eight tenths quicker than Alfa Romeo newbie Guanyu Zhou.

The Alpha Tauri of Pierre Gasly makes the top three with a time of 1:34.865, just 0.04secs ahead of Carlos Sainz in the Ferrari in fourth.

Toby Godfrey: Yes it's "just testing" but I expected to see Mercedes a bit higher by now... I don't think they are sandbagging as much as some would like to believe.

Image source, Getty Images

Our first little 'top pick' of the day was between Alpha Tauri's Yuki Tsunoda and Mick Schumacher of Haas.

We asked you which driver you thought would flourish in their second season in Formula 1?

The close klaxon has sounded and it was a tight one, but your choice went to Yuki Tsunoda, with 1,366 of your thumbs!

Well done, Yuki. We'll have another pick for you to get involved with soon...

Image source, .

Sergio Perez might not have done as many laps as other drivers during this morning session but that hasn't hindered the Red Bull.

Checo hits 15 rotations with a smooth, incident-free run to go top with a 1:33.105 on the C4 compound tyre.

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Getty Images

Are Mercedes in a bit of trouble? Ferrari's Carlos Sainz doesn’t think so - he made that clear on Friday. But after climbing out of his car on the same day, Lewis Hamilton insisted the world champions were having a "tough" test. Hamilton said Mercedes are still struggling with the aerodynamic "bouncing" or “porpoising” that appears to have afflicted them more than many other teams, even if all have it to some degree, and was not happy with the car.

"I mean, you can see on the on-board, tank-slappers left, right and centre," Hamilton said. "And then bouncing and bumping. It’s not quite happy at the moment. But we're trying to tame it."

When it was suggested to him that his rivals thought Mercedes were hiding their true pace, Hamilton said: "We would be really, really, really good if we were, like, having all these oversteer moments and having this tacky driving, just to hide our cars [pace]. It’s not the case. We have things that we're trying to get through. I think, as I said, others are struggling less but who knows? Maybe when we get to next week, we'll have a better understanding."

The yellow medium tyres have been bolted on to Hamilton's Mercedes for this run.

We haven't seen much of Lewis Hamilton but the seven-time world champion is back out on track to add his 25 laps and try and better his time of 1:36.217.

Rachel T: It is always impossible to get a true picture during F1 testing - unreliability is hard to hide, but everything else is smoke and mirrors. Bring on Bahrain qualifying next weekend!

Thanks for your comment, Rachel. The hashtag is open for any of your thoughts today. And Stoo G, I've got a Rocky reference (sort of) later on for you...

Williams are playing catch up after a fire in the rear brakes caused Nicholas Latifi to spin off during Friday's morning session.

The Canadian driver has clocked a 1:35.634 so far today to sit sixth on the timing sheets.

Alex Albon looked a lot calmer earlier on when having a chat with Sky Sports. The 25-year-old was in the commentary box when the drama with Latifi's car was unfolding.

Guanyu Zhou doesn't seem fazed by his rookie status as he knocks out another best lap, 0.175 seconds quicker than Sergio Perez.

Checo's Red Bull is glowing with green flow-vis paint as he completes a 12th rotation.

Let's nip across to the Haas garage for an update...

First year nerves should be out of the system now for Yuki Tsunoda and Mick Schumacher.

The 21-year-old Alpha Tauri man and 22-year-old Haas driver line up on the grid for their second seasons in Formula 1.

Other factors will likely be at play when it comes to where the pair will finish in the driver standings, but who do you think will flourish this year?

Press the left thumb if you think Yuki Tsunoda will continue to improve.

Or hit the right thumb if you think Mick Schumacher will show us his potential.

Image source, Getty Images

Guanyu Zhou is the new kid on the block this season but there are two drivers who have already experienced that feeling last year.

Now seems like a good time to do a thumbs up vote...

Guanyu Zhou in the Alfa Romeo is getting in as much preparation as possible before he takes part in his first Formula 1 weekend in seven days' time.

The Chinese driver is settling in well, as he finishes his 24th lap of the morning to go top with a 1:34.543.

More from journalist Albert Fabrega on Red Bull's fresh sidepods.

Plus, we can all pick up a bit of Spanish from these excellent tweets.

Gracias all round, Albert!

1. Sergio Perez (Red Bull, 6 laps) - 1:34.733

2. Pierre Gasly (Alpha Tauri, 21 laps) - +0.132s

3. Carlos Sainz (Ferrari, 18 laps) - +0.172s

4. Guanyu Zhou (Alfa Romeo, 21 laps) - +0.403s

5. Lando Norris (McLaren, 18 laps) - +0.771s

Andrew Benson
BBC Sport’s chief F1 writer

The new Red Bull parts that team principal Christian Horner called "a few bits and pieces" have emerged.

It turns out these were new side pods and a new floor. The bodywork changes slim down the lower part of the side pod to enlarge the already large cutaway even further, and cut away some of the upper part of the pod about halfway along, while the floor features a new section of waves and cuts at the widest point of the side pod.

Teams are using these to set up vortices that "seal" the floor edges and prevent air leaking into and out of the underfloor, thereby making the underfloor tunnels work better and maximising downforce. Sergio Perez went out on the C3 tyres and set the fastest time of the day so far on his first run.

You can see the differences in this tweet by the Spanish journalist Albert Fabrega: