Tomas Berdych needed two hours and three sets to overcome strong resistance from Russian qualifier Andrey Kuznetsov and reach the second round of the Monte Carlo Masters on Monday.
Berdych, a runner-up at the Country Club two years ago, converted only two of his 11 break points and rallied Kuznetsov 4-6, 6-3, 6-4. Berdych made the decisive break in the third game of the decider with a backhand winner down the line.
All six seeded players in action at the first big clay-court event of the season progressed to the second round: No. 12 Robert Bautista Agut, No. 13 Pablo Carreno Busta, No. 14 Alexander Zverev, No. 15 Albert Ramos-Vinolas, and No. 16 Pablo Cuevas.
Widely regarded as one of the most promising youngsters on the tour, the 19-year-old Zverev secured a convincing 6-1, 6-2 win over Italian veteran Andreas Seppi.
"I like playing on clay," Zverev said. "It's the surface I grew up on."
Zverev will next be up against either Feliciano Lopez or Daniil Medvedev.
Novak Djokovic, who has been drawn in the same half of the draw as nine-time champion Rafael Nadal, will start his campaign on Tuesday against Gilles Simon of France. Djokovic has been struggling with injuries and recently withdrew from the Miami Masters with a right elbow complaint.
"The elbow is fine now," Djokovic said. "I've been training for the past couple of weeks, playing Davis Cup, and making the transition to clay that's very demanding for the body. I was skeptical of how my elbow would react to the heavy balls on clay, but it's been good so far."