US Open champion Emma Raducanu rallied back from 2-5 down in the first set before switching gears to post a 7-6 (7/3), 6-0 result against Czech Republic's Tereza Martincova and set up an intriguing second round with fellow 19-year-old Marta Kostyuk.
Playing just her second ever tour-level tournament on clay, the British No.9 seed converted all four break point opportunities she created and saved six of seven break points on her own serve on her way to the 96-minute win - her second success over Martincova in two weeks.
"I was definitely just getting adjusted to the courts and the surroundings," Raducanu said of the opening set.
"She also came out swinging very well, so I was definitely feeling a little bit like I've got to dig in here. I'm very proud of the way that I managed to make the most of what I had on the day, and then I definitely settled in the second set."
Naomi Osaka passed her first clay-court test of the season with flying colours, snapping the nine-match winning streak of Anastasia Potapova with a smooth 6-3, 6-1 victory to reach the second round.
The former world No.1, who received entry into the tournament via a wildcard, needed just 61 minutes to ease past Russia's Potapova, who was coming off a title run in Istanbul last week and won nine consecutive matches on clay coming into their showdown.
"I wouldn't say it was an easy match, I feel like I just adjusted a little bit. It's really good to be playing on clay again," said Osaka.
She next takes on home favourite Sara Sorribes Tormo or last year's Roland Garros runner-up Anastasia Pavlyuchenkova.
Earlier in the day, former US Open champion Bianca Andreescu recorded her first top-50 victory on clay with a 6-4, 3-6, 6-0 dismissal of American Alison Riske.
"I have to say that compared to last year, this year is much, much better. I was in quarantine last year because I caught Covid, so to be here actually playing the tournament this year is incredible," said Andreescu, who takes on Australian Open finalist Danielle Collins in the second round.
No.4 seed Maria Sakkari survived a tough two-hour 30-minute duel with American power-hitter Madison Keys, saving five out of seven break points en route to a 6-7(8/10), 6-3, 6-4 result.
"Obviously Madi is a big-hitter, I think conditions suit her well here," Sakkari told reporters in Madrid on Friday.
"When I saw the draw, I was like, 'F***, that's a first round', you know. There are a lot of tough first rounds here.
"I just trusted my game, first set we couldn't break each other so it was pretty even. I was unlucky in a few moments in the tiebreak. But overall I think it was a very positive match to get myself back into the winning feeling."
