Reigning champion Novak Djokovic and former titlist Juan Martin del Potro were a pair of second-round winners on a hot Friday at the U.S. Open.

The second-seeded former world No. 1 Djokovic drubbed Brazil's Rogerio Dutra Silva 6-2, 6-1, 6-2 in 1 hour, 39 minutes at Ashe Stadium, where the temperature was above 90 degrees on Day 5.

Djokovic currently holds two of the four Grand Slam titles, as he also won this year's Australian Open in addition to his 2011 U.S. Open championship when he beat Rafael Nadal in the final at the USTA Billie Jean King National Tennis Center.

The five-time major champion is also a two-time U.S. Open runner-up (2007, 2010).

The seventh-seeded del Potro got past 20-year-old American Ryan Harrison 6-2, 6-3, 2-6, 6-2 in 2 hours, 34 minutes at Armstrong Stadium.

Harrison is now 0-15 lifetime against top-10 ATP players.

The 6-foot-6 Del Potro stunned Roger Federer in five sets in the 2009 U.S. Open final.

Spanish star David Ferrer was also a second-round winner on Friday.

The fourth seed moved on in straight sets against Dutchman Igor Sijsling, but the tight third went to a tiebreak, as the gritty Spaniard settled for a 6-2, 6-3, 7-6 (14-12) decision on the Grandstand court.

Ferrer advanced in 2 hours, 27 minutes, breaking Sijsling four times en route to the round of 32.

Nifty 13th-seeded Frenchman Richard Gasquet moved on by easily beating Stanford University's Bradley Klahn 6-3, 6-3, 6-1, while 14th-seeded Ukrainian Alexandr Dolgopolov drove out former Aussie Open runner-up Marcos Baghdatis of Cyprus 6-4, 3-6, 6-0, 7-6 (7-5).

Former world No. 1 and 2001 U.S. Open champ Lleyton Hewitt stayed alive in the draw with a gutsy five-set victory over left-hander Gilles Muller of Luxembourg, 3-6, 7-6 (7-5), 6-7 (5-7), 7-5, 6-4, in 4 hours, 35 minutes. The two-time major champion Hewitt will face Ferrer in his next outing.

Meanwhile, 22-year-old American Steve Johnson reached the third round by overcoming talented Latvian Ernests Gulbis 6-7 (3-7), 7-6 (7-5), 6-3, 6-4. Gulbis launched 24 aces in a losing effort.

The former USC Trojan Johnson is a two-time NCAA singles champ.

Also advancing was Argentine Leonardo Mayer, who took out former top-10 star Tommy Robredo of Spain 6-1, 6-4, 4-6, 7-5. Mayer is rewarded with a third- rounder against his fellow countryman del Potro.