Emma Raducanu shakes off jet lag to win late-night opener in Washington

The 21-year-old British number three won 6-2 3-6 6-4 against the eighth-seeded Belgian in a match that finished after 11pm in the US capital.

Raducanu won their only previous clash at Wimbledon earlier this month for the loss of only three games and looked on course for a similar result as she won five straight games to sweep through the first set, before feeling the effects of her travel to the US.

"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'."

Mertens fought back in the second set, cutting down on the errors and making the most of her only break serve to level the match after the former US Open champion had led 40-0 in the sixth game.

Raducanu broke early in the final set, but could not make the most of a 3-1 lead as Mertens broke back and saved two break points to level at 3-3.

Raducanu saved five break points of her own before breaking again, only for Mertens to strike back in the next game as the Briton served for the match.

But it only delayed the outcome, with Raducanu moving to match point with a backhand volley and sealing the win courtesy of Mertens' 11th double fault.