Juan Martin del Potro closed out countryman Leonardo Mayer in a 20-point tiebreaker, which included a shot by Mayer that bounced off the net post while headed wide and landed in, to return to the fourth round of the U.S. Open for the first time since his 2009 title run.

The seventh-seeded Argentine won 6-3, 7-5, 7-6 (9) in 3 hours, 20 minutes Sunday. Del Potro was unable to defend his championship in 2010 because of right wrist surgery. Last year, he lost in the third round.

Del Potro is coming off a bronze medal at the Olympics, defeating Novak Djokovic in the third-place match in London.

The 63rd-ranked Mayer has never reached the fourth round at a major tournament or defeated a top-10 player.