Former champ Muguruza knocked out by Kostyuk

Kostyuk was touted for a big future when in 2018 at age 15 she became the youngest player since Martina Hingis to reach the Australian Open third round.

The Ukrainian world No.81 had admitted to struggling with the weight of expectation since but showed nerves of steel on Court Simonne-Matthieu on Monday as she landed her maiden top 20 victory over the No.12 seed.

After conceding the opening set in just 35 minutes, Muguruza called a medical time-out to have her back treated. She looked to have turned the tables when she jumped to a 3-1 lead in the second, however, she was clearly trying to shorten the points as the match wore on.

The Spaniard proceeded to lose four straight games before she saved a match point on serve at 3-5 to stay alive. It merely delayed the inevitable as Kostyuk made good on her third match point after 83 minutes.

After reaching the final in Doha and winning Dubai, the Spaniard has failed to pass the round of 16 in her subsequent four events now, having struggled with a left thigh injury in the switch from hard courts to clay.

Earlier, Roger Federer enjoyed a victorious return to Grand Slam play as he notched his first win on clay in two years in his first match at a major since the 2020 Australian Open with a 6-2, 6-4, 6-3 rout of qualifier Denis Istomin.

The Swiss' last match-win on the red dirt came in the Roland-Garros quarter-finals in 2019 and he skipped the majority of 2020 to recover from two knee surgeries.

The 39-year-old, seeded No.8 this fortnight, needed just 93 minutes to topple Istomin and next squares off against familiar foe and former US Open champion Marin Cilic.

Federer faced zero break points against Istomin and dropped just four points on his second serve.

The 2009 Roland-Garros champion downplayed his chances coming into the tournament given his lack of match-play but sent out an impressive warning with his commanding display in his opener.

Bianca Andreescu suffered her first-ever tour-level defeat on clay as she fell to Slovenian Tamara Zidansek in a three-hour 20-minute tussle 6-7(1), 7-6(2), 9-7 in opening-round action at Roland-Garros on Monday.

The Canadian No.6 seed had only ever contested three tour-level matches on clay coming into the tournament as injuries have wreaked havoc with her playing schedule for the past couple of seasons.

Zidansek, a 23-year-old ranked 85 in the world, scored her first career win at Roland-Garros, having lost her openers on her two previous visits here.

>> DAY 2 RESULTS

The topsy-turvy clash witnessed a combined 30 break point opportunities for both players and saw Andreescu, who withdrew ahead of her Strasbourg quarter-final last week citing an abdominal issue, hit eight double faults and 63 unforced errors.

Zidansek, whose first passion was snowboarding before venturing into tennis, next takes on American Madison Brengle., who defeated in-form Colombian qualifier Maria Camila Osorio Serrano.

Belinda Bencic brought more delight to the Swiss fans as she joined Federer in round two by knocking out last year's semi-finalist Nadia Podoroska 6-0, 6-3 and next plays Daria Kasatkina or Misaki Doi.

Home favourite and former quarter-finalist Caroline Garcia started her Roland-Garros 2021 journey with a smooth 6-3, 6-1 dismissal of Germany's Laura Siegemund.

Garcia, who needed just 67 minutes to advance on Court Suzanne-Lenglen will meet Slovenian Polona Hercog in round two.

Norwegian No.15 seed and recent Geneva champion Casper Ruud wobbled in the first set before skipping past Frenchman Benoit Paire 5-7, 6-2, 6-1, 7-6(4), to arrange a second-round date with Poland's Kamil Majchrzak or French wildcard Arthur Cazaux.

American No.32 seed Reilly Opelka continued to showcase his clay-court credentials with a smooth 6-3, 6-2, 6-4 win over Slovakian Andrej Martin, who just a few days ago stretched Novak Djokovic to three sets in the Belgrade semi-finals.

The 23-year-old Opelka, who next plays Jaume Munar or Jordan Thompson, will be joined in the second round by his fellow American, former Roland-Garros junior champion Tommy Paul, who survived a marathon battle with Australian Christopher O'Connel 6-2, 6-4, 4-6, 4-6, 10-8.

Paul's reward is a second-round test against No.2 seed Daniil Medvedev.