Britain's Katie Boulter beat Taylor Townsend in straight sets to set up a second-round clash with world No 5 Jessica Pegula at the Mutua Madrid Open.
Boulter overcame the American 6-4 6-2 in an hour and 33 minutes to record her second career win in Madrid.
The Brit improved to 10-2 in tour-level matches this year against players ranked outside the top 50.
She set up 14 break point opportunities in a commanding performance against the Townsend serve, breaking four times in the match in further signs of her growth on clay.
"I feel like my confidence is building on this surface," Boulter told Laura Robson on Your Site. "I do think I'm getting stronger and believing more coming out of the corners. I think I'm improving match by match.
"I enjoy the competitive nature of this sport, which is being stubborn and not letting go or losing focus. I think that was the difference today, I dug in in the big moments, trusted my shots and then I think in the second set I stepped it up a bit and played better tennis."
While clay hasn't been her favoured surface in the past, the Briton won her first title of the surface at last year's WTA 125 Paris and reached the quarter-finals in Rouen last week.
Boulter beat Pegula at the 2024 United Cup, before the American levelled their head-to-head record at one apiece in the semi-finals of the Billie Jean King Cup last year.
Pegula is coming off a successful defence of her Charleston Open title having beaten Yuliia Starodubtseva 6-2 6-2.
"She's a great player, she's very in form and plays well on every surface," said Boulter. "It's going to be a massive challenge for me but I have nothing to lose at the end of the day. I can have a go at someone on a surface I don't love, and I'm going to try and play my way."
The win also followed the announcement that Boulter will be teaming up with 23-time singles and doubles Grand Slam champion Venus Williams.
They will open against Xinyu Jiang and Yifan Xu of China in the first round on Friday.
"She's an absolute icon, I'm so excited to be playing with her," said Boulter. "It's going to be a dream come true for a little girl who once looked up to her."
Boulter will face Pegula in the second round of the Mutua Madrid Open on Friday 24 April - watch live on Your Site Tennis.
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