Top-seed Rafael Nadal overcame a sluggish start to beat Fernando Verdasco 3-6, 6-1, 6-1 in the first round of the Hamburg Open.
Nadal was playing his first match since losing to Dustin Brown in the second round of Wimbledon.
The former world number one has fallen to 10th in the rankings following injury and poor form.
In the all-Spanish match, Nadal appeared to have trouble adjusting to clay and finding his timing.
But his game picked up noticeably in the last two sets. Verdasco saved one match point but then hit the net with a backhand to hand Nadal the win.
Nadal's last match on clay was the quarterfinal loss to Novak Djokovic at the French Open.
"For my mentality, it is important to finish the match better than how I started," Nadal said.
"To be able to make that change during the match was a very positive thing to me."
The match was played under the court's canvas cover because of rain.
Second-seed Tommy Robredo also needed three sets to advance, rallying for a 6-7, 6-4, 6-2 win over wild-card entry Alexander Zverev.
Third-seeded Roberto Bautista Agut, fourth-seeded Andreas Seppi and sixth-seeded Juan Monaco all advanced into the second round.