Rafael Nadal's hopes of winning a record-breaking eighth French Open title remain on track, but only after the Spaniard was given an opening set scare by Martin Klizan.
The powerful left-handed Slovakian, who just missed out on being seeded, surprised Nadal by claiming the first set before the third seed rallied to win the next three 4-6 6-3 6-3 6-3.
The 11-time Grand Slam winner, who was also given a major fright in the first round against Daniel Brands, struggled with the moist conditions on Court Suzanne Lenglen before prevailing in two hours and 44 minutes.
Klizan came out swinging in the opener and brought up set point with a second serve ace before confidently taking it in 40 minutes.
Nadal responded immediately by surging 4-0 ahead in the second but 23-year-old Klizan remained a threat and recovered one of the breaks of serve.
The Mallorcan took the second set and then moved a break ahead in the third but wobbled at 3-2 when the 35th ranked Klizan earned two break points, only to squander his chance to draw level.
Klizan's challenge then faded and Nadal, without looking totally convincing and carelessly dropping serve late in the fourth set, secured his spot in the next round.
Italy's dangerous claycourter Fabio Fognini is already through and waiting for defending champion Nadal in the third round on Saturday having had an extra day's rest.