Stan Wawrinka avoided becoming the first defending champion to lose first round at the French Open on Monday when he battled past combative Lukas Rosol in five tough sets.
Third seed Wawrinka fired 56 winners but committed 46 unforced errors and saved eight break points to book a second round clash against Japan's Taro Daniel.
Wawrinka, 31, had defeated 59th-ranked Rosol in the semi-finals of the Geneva clay-court tournament just last Friday.
But Rosol went into the match on a chilly Court Philippe Chatrier with the pedigree of having famously stunned Rafael Nadal at Wimbledon in 2012.
That free-swinging masterclass almost paid dividends again Monday but once he had let slip two break points at 2-2 in the fourth set, his hopes slowly slipped away.
Spanish fourth seed Garbine Muguruza was also struggling on Court Suzanne Lenglen, coming back from a set down to defeat Slovakia's Anna Karolina Schmiedlova 3-6, 6-3, 6-3.
Muguruza, who has made the quarter-finals for the last two years, will take on French wildcard Myrtille Georges, the world number 203, for a place in the last 32.
But the 22-year-old Wimbledon runner-up was far from impressive in the two and a half hour encounter.
After dropping the first set, Muguruza had to save nine break points just in the opening game of the second set.
She then allowed her 37th-ranked opponent, who has won just one match all year, to claw her way back from 0-4 down to 3-4 in the decider before the Spaniard settled herself to see out the win.
Muguruza fired 44 winners but hit 53 unforced errors and had to save 17 of 21 break points. Play started two and a half hours late Monday because of more rain with 12 of the 66 scheduled matches pushed back to Tuesday.
However, there was plenty of time for notable firsts. Qualifier Cagla Buyukakcay beat Aliaksandra Sasnovich of Belarus 5-7, 7-6 (7/2), 6-2 to become the first Turkish woman in the Open era to reach the second round of a Grand Slam.
The 26-year-old Buyukakcay, ranked at 83, had earlier this clay-court season become the first Turk to win a WTA title when she triumphed in Istanbul.
Japan's Naomi Osaka won her first match at Roland Garros with a 6-4, 7-5 triumph over Latvian 32nd seed Jelena Ostapenko.
Elsewhere, Canadian eighth seed Milos Raonic, a 2014 quarter-finalist, defeated Serbia's Janko Tipsarevic 6-3, 6-2, 7-6 (7/5). Tipsarevic, ranked at 686, was playing his first Roland Garros since 2013 after being treated for a benign tumour on his left foot.
Japanese fifth seed Kei Nishikori beat Italy's Simone Bolelli 6-1, 7-5, 6-3 on Court Philippe Chatrier on Sunday.
Victory gave the 26-year-old Japanese his 50th Grand Slam win. Russia's Svetlana Kuznetsova, the 2009 champion, won her resumed match against Yaroslava Shvedova of Kazakhstan 4-6, 6-1, 6-4.
There was also a win Monday for Croatia's Mirjana Lucic Baroni who first played the main draw in Paris in 1999. The 34-year-old knocked out 33-year-old Daniela Hantuchova of Slovakia 6-1, 6-2.