Nadal, the World No. 1, returned effectively and limited Stepanek to 32 percent of his second-serve points won, breaking him six times.
He also won 62 percent of his first-serve points and 57 percent of his second-serve points, yet he was still broken three times in the match.
The Spaniard has a 5-1 record against Tsonga, with the Frenchman’s only victory coming at the 2008 Australian Open semifinals.
Both players earned two breaks of serve in the match, although del Potro had far more break-point opportunities.
There were no breaks in the first set, although del Potro had three chances, and the Argentine had seven more opportunities in the second set. Mannarino had only two break points in the match, and he capitalized on both of them.
The difference may have been in how each man served. Del Potro hit his first serve well, winning 77 percent of his first-serve points compared to his opponent’s 62 percent. Yet he struggled on his second serve, winning 44 percent of those points compared to Mannarino’s 70 percent.
Del Potro, the 2009 US Open champion, is on his way back from an injury that saw him miss the 2010 season and drop to almost No. 500 in the rankings.
He may still be rusty, but Mannarino has proven that he can beat top competition on the grass. In the second round, the Frenchman defeated sixth-seeded Gilles Simon in three sets.
Mannarino will face the winner between American Sam Querrey and James Ward, the
216th-ranked Englishman who upset fourth-seeded Stanislas Wawrinka in the second round.
Querrey and Ward's match was postponed because of darkness after they split sets.