Former champion Juan Martin del Potro outslugged a gritty Guillermo Garcia-Lopez in a contentious four-set match to reach the second round of the US Open on Wednesday.

Argentine del Potro, who won his only Grand Slam at Flushing Meadows in 2009, beat the 74th-ranked Spaniard 6-3, 6-7 (5), 6-4, 7-6 (7) on his fourth match point.

"Felt good because I won the big battle for the first round," del Potro said.