Emma Raducanu had to fend off jet lag as she overcame Elise Mertens in the first round at the Washington Open.

Making her first appearance since she lost in the last 16 at Wimbledon, Raducanu prevailed 6-2 3-6 6-4 over Mertens, who she also defeated at the All England Club, on Monday.

The 21-year-old elected to skip the Olympics to focus on her hard-court form and prepare for the US Open, which she won in 2021.

Raducanu's Washington campaign started with a stern test against Mertens, with the match dragging on well beyond 11pm local time.

And Raducanu conceded it was a struggle as she grappled with jet lag.

"I was playing some pretty good tennis in patches throughout, especially in the first set and moments in the third set," she said.

"I lost some focus in the second. It's not easy playing at 11:30. I got here Thursday night so I'm still jet-lagged.

"I was telling myself, 'I'm not leaving. This is not happening. You're not losing this match'.

"I've been training and playing so good in practice. I've been really on it. So on the court, I was telling myself: 'You've been so focused for so long. There's no way you're not going to try right now. You're going to fight until the very end. You didn't put all that work in for nothing'."

"I'm happy with how I pulled myself out of it, but I do need to focus."