MADRID — Felix Auger-Aliassime fought through a tight match on Sunday to beat fellow Canadian Denis Shapovalov in the first round of the Mutua Madrid Open.

Auger-Aliassime took a 6-2, 7-6 (7) victory over his long-time friend following a close second set.

The 18-year-old Montreal native converted three of his nine break points and clinched his fourth match point after Shapovalov sent a forehand shot wide during the tie break.

Auger-Aliassime will face No. 2 ranked Rafael Nadal in the second round of the ATP 1000 clay-court event on Tuesday.

Nadal, who had a bye in the first round, is considered the best clay-court player in the world.

The Spanish tennis great is looking to clinch his 50th tournament victory in his home country's capital.

Auger-Aliassime has rocketed up the world tennis rankings this year, thanks in large part to some strong results in South American clay-court events, highlighted by a runner-up showing at the Rio Open.

He comes into the Madrid event ranked 30th. Shapovalov, of Richmond Hill, Ont., sits at No. 20.

Sunday marked the second time Auger-Aliassime and Shapovalov have met in a tour event. Last year they played in the first round of the U.S. Open in New York, where Auger-Aliassime retired early due to a racing heart.

The pair are off to slow starts in the European clay-court season after both reached the semifinals in March at the Miami Open, a Masters 1000 hard-court event. Shapovalov has lost his past three matches, while Auger-Aliassime had dropped two of three going into the Madrid Open.

Sunday also saw Germany's Jan-Lennard Struff beat Nick Kyrgios of Australia 7-6 (4), 6-4 in first-round play.

On the women's side, Naomi Osaka and Simona Halep won their opening matches while Garbine Muguruza was upset by Petra Martic of Croatia on Sunday.

The top-ranked Osaka, the reigning U.S. Open and Australian Open champion, hit 43 winners, including eight aces to beat 2016 finalist Dominika Cibulkova 6-2, 7-6 (6).

"For me, I'm just happy to get through it,'' Osaka said. "I feel the most nervous during the first round and to play against Cibulkova was kind of tough for me, especially on clay.''

Osaka will face Sara Sorribes in the second round after she got past fellow Spanish wild card Lara Arruabarrena.

Martic ousted two-time grand slam winner Muguruza 7-5, 7-6 (2) a week after the Croat won her first career title in Istanbul.

Two-time Madrid champion Halep brushed off Russian qualifier Margarita Gasparyan 6-0, 6-4.

Milos Raonic and Bianca Andreescu, Canada's top-ranked singles players on the men's and women's sides, are not playing in the Madrid Open because of injuries.

— With files from The Associated Press.