Rafael Nadal and Roger Federer opened their clay-court seasons with comfortable second-round victories at the Monte Carlo Masters 1000.
Federer, without a title since October, had originally decided to skip the famous event but accepted a late wildcard as he looks for some form.
And the world number two came through 6-4 6-4 against Seppi to reach round three of the Masters 1000 tournament.
Nadal had far too much for Argentina's Juan Ignacio Chela, winning 6-2 6-3.
The Spaniard, going for his fifth straight title in Monte Carlo, stormed 4-0 ahead with some blistering play before Chela recovered to 4-2 and a 0-40 lead.
Nadal regained his focus to save all three break points and powered through the set before letting another early lead slip in the second.
We've been playing on hard court now for nine months - you never see a bad bounce
Roger Federer
After dropping two games from 3-0, the world number one again gathered himself to grab one more decisive break and see out the match.
Nadal was critical of his performance following his victory and admitted he would have to improve in certain areas to win his fifth straight title in Monte Carlo.
"I had some tough moments during the match," Nadal said.
"I played some games well, I had some terrible games... (I was) up and down during all the match.
"I have to improve my concentration in the next match. That's the important thing."
Elsewhere on Wednesday number five seed Juan Martin Del Potro suffered a shock 4-6 6-1 6-4 defeat, losing to Croatian Ivan Ljubicic .
But number six seed Nikolay Davydenko was safely through beating Croatian Ivo Karlovic in straight sets 6-4 6-3.
British number one Andy Murray beat Victor Hanescu on Tuesday and in the last 16 he will play Italian Fabio Fognini , who thrashed Marin Cilic 6-2 6-0.
Federer went into his opening match with a 4-0 record against Seppi, the world number 40, but potentially vulnerable after a bad loss to Novak Djokovic in Miami last time out.
But the 27-year-old, who married his long-term girlfriend Mirka Vavrinec last week, made the first breakthrough with some heavy forehands in game nine after saving two earlier break points.
Two magnificent games followed from the 13-time Grand Slam champion as he served out the set and broke at the start of the second, going on to seal a comfortable victory.
606: DEBATE
Did anyone realise that Federer has lost only 4 times in 2009? Twice to world #4 Once each to world #1 and #3
Aussie_Ahmed
"I am very happy to have won my first match on clay," he said. "It takes some time to adjust to the surface, the rebounds and the sliding.
"We've been playing on hard court now for nine months - you never see a bad bounce.
"So all of a sudden you're a little bit worried, sometimes hitting half volleys because they can bounce onto your frame."
Federer will play compatriot Stanislas Wawrinka in the third round after the 13th seed beat Argentina's Martin Vassallo Arguello 2-6 7-5 6-2.
In other matches, seventh seed Fernando Verdasco defeated Philipp Kohlschreiber 6-3 6-4, and 11th seed Nikolay Davydenko returned from an injury lay-off to beat Ivo Karlovic 6-4 6-3.
Argentina's David Nalbandian , the 12th seed, beat Spaniard Marcel Granollers 4-6 6-3 6-1, and Spanish 10th seed David Ferrer destroyed Marc Gicquel 6-1 6-0.
