Oh Jamie! Stunning backhand volley winner and Judy Murray is on her feet in the stands.

Deuce.

A brilliant forehand smash from Chan and they have a break point.

Michael Venus attempts a backhand winner but drives it into the net.

Back to 15-15, though, as Murray hits a backhand volley too long.

A backhand winner gives the top seeds a 30-15 cushion, but Murray produces a backhand volley winner and we're back on level terms. 30-30.

Breaks of serve all over the shop in the second set.

Chan and Venus lose the break with a forehand smash forced error.

GAME ON!

Image source, EPA

Cheeky little forehand volley winner there from Venus, but Chan undoes the hard work with a forehand unforced error.

Murray wins the point with a forehand volley winner. Two break points.

Mattek-Sands is absolutely on fire today. A simple backhand lovely winner draws them level on 30-30.

She produced an excellent performance at the net, and then goes on to miss what should have been an easy shot, which goes long.

She then attempts a forehand smash, but drives it into the net.

Chan and Venus break straight back.

We're 35 minutes into the action on Ashe under glorious blue skies, and Mattek-Sands and Murray are proving dominant so far against the top seeds.

They've done it!

That's the first time Chan and Venus have been broken three times in this mixed doubles tournament.

Break point now as Michael Venus loses the point with a double fault.

A fantastic forehand winner from home favourite Mattek-Sands pulls back a point for the pair, as they trail 30-15.

Deja-vu as she does the same again, and it's 30-30.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Numbers have arrived already on Ashe. That’s the pull of Bethanie Mattek-Sands (and Jamie Murray).

Unsurprisingly they have the backing of the American crowd, who have pretty much filled the lower tier of the near 24,000-capacity bowl.

Image source, BBC Sport

Jamie Murray. Bravo my friend.

Brilliant work at the net as he hits a backhand volley winner to take the first set.

It's the first set Chan and Venus have dropped this whole tournament, and what a time to do it.

Two break points now for Chan and Venus after back-to-back forehand errors from Murray and Mattek-Sands.

But they win the break with a backhand volley winner. One break point.

Murray produces a stunning forehand winner and we're back to deuce.

Mattek-Sands is serving for the set.

Murray attempts a backhand volley but it goes into the net for 15-15.

A forehand volley forced error from Mattek-Sands reduces their lead to 40-30.

Jamie Murray produces a brilliant backhand volley winner right down the middle of Chan and Venus.

5-2.

Another unforced error kicks off Chan and Venus' service game, but Mattek-Sands hits a forehand too long.

Chan seems frustrated as she drives a backhand into the net, before a brilliant forehand winner from Mattek-Sands.

Two break points.

Chan and Venus currently have double the number of unforced errors, with eight to Murray and Mattek-Sands' four.

The reigning champions hold their serve with no problems at all, with the exception of a double fault from Murray to salvage a point for the top seeds.

A stunning big return from Mattek-Sands gives herself and Murray a break point.

They successfully convert the first break point of the match after an unforced error from the top-seeds.

3-2.

Michael Venus hits an ace to kick off the next service game, but follows up with a forehand volley into the net.

Murray produces a brilliant forehand winner down the T to make it 30-15 to the 2018 champions.

Michael Venus hits a backhand into the net, and another forehand forced error gives Murray and Mattek-Sands the game.

2-2