British Davis Cup player Colin Fleming on BBC Radio 5 live sports extra:  "Since that 3-2 game, both players have been wrestling for the momentum. When Watson had those three points, they were all played on Davis's terms. And when Davis had the break points, they were again played on her terms. That's the difference - Davis is stepping up and taking control at the key moments."

Watson moves quickly to 30-0 - but then she nets a backhand return and gets into trouble on the next rally, allowing Davis to stretch her in a rally before thumping a volley past her. 30-30. Watson responds with an ace, but then misjudges a forehand into the net at the end of another long rally - and is taken to deuce on her own serve for the first time in the match.

Davis earns a break point with a clever forehand down the line that Watson nets, and a cross-court forehand error from the Briton hands the American the game. Davis will now serve for the set - and that has come out of nowhere.

And yet, Davis holds comfortably. A neat backhand winner for a 30-0 lead is followed by an ace. Watson responds with a good cross-court return, but Davis finishes the game with a second serve that Watson returns into the net. Good recovery from Davis there after the difficulties in her last service game.

Former US Open doubles champion Andrea Hlavackova on BBC Radio 5 live sports extra: "That was a good hold for Heather. Sometimes, when you have a chance to break and don't take it, you can then lose your own next service game because your momentum has gone. But she has kept up the pressure."

Image source, Getty Images

So, after a cagey opening, the match is opening up a little. Watson still looks in control of the rallies on her own serve, with a lovely backhand winner finishing one exchange for a 40-15 lead, before finishing with a forehand winner for a confident hold. Over to you, Lauren...

(* denotes next server)

Watson sees an opening and pounces, pinning Davis back on the baseline in a series of rallies. There's a forehand winner and a couple of Davis errors, and suddenly Watson has a 0-40 lead and three break points. Davis takes her time, composes herself, and saves all three. Some superb work by the 21-year-old American - engineering her points well to save the second and third break points. The rallies are getting longer as we go to deuce; Watson saves one game point, but Davis takes her second chance to hold with a cross-court winner as a Watson drop shot is a bit short.

Watson, though, is stepping up the pressure. This is encouraging from the British number one.

(* denotes next server)

Piers Newbery
BBC Sport at Flushing Meadows

Watson has had some horror draws at Flushing Meadows, so her 0-4 record is a bit misleading, but she had a chance to progress last year against an apparently out-of-form Sorana Cirstea. In the event, the Romanian won 6-1 6-1 and a year on Watson was still bemused. "I don't know what happened there," she said. Facing Davis represents another real chance to break her New York duck.

Watson isn't making much headway on Davis so far, but her serve is secure, so she can afford to be patient for now. The Briton is well in control, holding to 15 this time, and clinching the game with a rally that ends with Davis hitting a forehand wide.

(* denotes next server)

Image source, Getty Images

The first big rally of the match, a 21-shot effort, ends with Davis coming out on top for a 30-0 lead, before Watson hits back with an excellent forehand return. It's the only point Watson has won against serve so far - Davis is hitting the ball well, as she holds.

Solid serving once more from Watson, with Davis not giving much in response so far. The Briton seals the game with an ace that clips the line - Davis challenges, but Hawk-Eye calls it good, and we remain with serve.

(* denotes next server)

Piers Newbery
BBC Sport at Flushing Meadows

A cloudy start to the day in New York is threatening to turn into a scorcher this afternoon, so Watson might benefit from the early start. I happened to be the person to deliver the news on Saturday that she would be playing first on day one. "Am I?" she said with a smile. "That's OK. I like it, because I know exactly when I'm going to play."

Lauren Davis seems to be having a bit of hair trouble. The American has long brown locks under a sun visor, and needs to go to her chair to fix herself back into place. It doesn't stop her holding to love, though. A couple of unforced errors from Watson in that game, and we're all square.

(* denotes next server)

Former US Open double champion Andrea Hlavackova on BBC Radio 5 live sports extra:  "You can tell Heather is a bit nervous going into this match. But I think all the girls are going into a Grand Slam. You walk into the locker room and notice the girls are bit more on edge than usual.

Image source, Getty Images

A confident start from Watson soon takes her to 40-0, before a double fault gives Davis a glimmer, but the Briton sees the game out without too much trouble.

(*denotes next server)

Lauren Davis, dressed in a bright red/pink outfit, takes a swig of drink. Heather Watson, in a blue outfit, adjusts her luminous yellow headband. The players take their positions, and we're ready to go. It's Watson to serve...

The winner of today's match is likely to face a second-round meeting with Russian 13th seed Ekaterina Makarova - a semi-finalist at Flushing Meadows last year. Makarova is facing unseeded Brazilian Teliana Pereira today.

Here's what Heather Watson said to BBC Sport as she prepares to step back on to the Grand Slam stage for the first time since Wimbledon.

"You have to get the motivation back after such a big match on a big stage," she said.

"You've got to find that fire and that fight every single week, no matter how loud or quiet it is.

"Apart from the few days after the [Williams] match, I haven't thought about it at all really. I'm not looking back now, I'm looking ahead."

The players are out on Court 17: Lauren Davis bounds out first, with Heather Watson looking relaxed just behind her. Time for a bit of warming up, and then we're ready. Let's hear from Watson...

Image source, EPA

Davis, of the United States, is ranked below Watson - she's 84th in the world. The 21-year-old has been to the third round at Wimbledon and the Australian Open, though, and is renowned for her speed around the court. The Briton will have to be on her guard.

Today, though, as the US Open gets under way, the 23-year-old is chasing a little bit of history. She has never been beyond the first round at Flushing Meadows before - but neither has her opponent, Lauren Davis.