Rafael Nadal dropped his first set at the Barcelona Open since 2015 but recovered to beat Leonardo Mayer in his opening encounter.
Nadal has never lost consecutive tour-level matches on clay but that looked a distinct possibility when, four days after a shock semi-final loss to Fabio Fognini in Monte Carlo, he again struggled to find his form.
The 32-year-old has won the title in Barcelona a record 11 times, winning all his matches in straight sets for the past three years.
Nadal failed to serve out the opening set and saw three set points saved by Argentinian Mayer, the world number 63, who came out on top in the tie-break.
But Nadal broke serve immediately at the start of the second set and grew in confidence as the match went on before clinching a 6-7 (7) 6-4 6-2 victory.
Nadal was downbeat afterwards, saying on atptour.com: "It wasn't the best start. Not the best feelings out there this afternoon, but I found a way to keep going and to win the match. Today that's the main thing.
"(Mayer) competes well against everybody but probably today (the problem) was not that he competed very well against me. I was not competing that well."
In the third round Nadal will try to beat compatriot David Ferrer for the 26th time in 32 meetings. Ferrer will retire after the Madrid Open next month but was in fine form in a 6-3 6-1 win against 15th seed Lucas Pouille on Wednesday.
Sixth seed Karen Khachanov's difficult season continued with a 6-2 7-6 (4) loss to Guido Pella, while fellow seeds Denis Shapovalov, Gilles Simon and Pablo Carreno Busta also fell.
Seventh seed Daniil Medvedev dropped the second set but recovered to beat Albert Ramos Vinolas 6-3 2-6 6-1 and Canadian youngster Felix Auger-Aliassime saw off Malek Jaziri 6-3 7-6 (7).
Grigor Dimitrov was given a predictably tough test by Fernando Verdasco but the 13th seed came through 6-2 6-7 (4) 6-3.
Local wild card Attila Balazs caused a shock in the second round of the Hungarian Open in Budapest by upsetting sixth seed and 2018 runner-up John Millman 6-4 2-6 6-2.
There was a notable first ATP win, meanwhile, for 17-year-old Italian Jannik Sinner, who saw off Hungary's Mate Valkusz 6-2 0-6 6-4.
