Updated

Wimbledon champion Roger Federer and former Wimbledon titlist Novak Djokovic secured berths in the quarterfinals at the London Olympics tennis event.

The world No. 1 Federer was tested in the first set en route to a 7-5, 6-3 third-round victory over Uzbekistan's Denis Istomin on Court 1 at the All England Club, where the Swiss icon has captured seven Wimbledon championships, including his most-recent one only four weeks ago. The match was interrupted by rain, with the score tied at 5-all in the first set.

Federer moved on in 81 minutes despite committing an uncharacteristic 24 unforced errors over two sets. The Swiss great, however, was broken only once en route to victory.

The 30-year-old Federer's quarterfinal opponent will be seventh-seeded Serb Janko Tipsarevic or 10th-seeded American John Isner.

Federer would complete a career "Golden Slam" with a gold-medal performance this week.

The second-seeded Djokovic, who recently lost the No. 1 ranking to Federer, needed all three sets to stave off former top-ranked star Lleyton Hewitt of Australia, 4-6, 7-5, 6-1. The reigning Australian and U.S. Open champion Djokovic fired 16 aces before getting past Hewitt, who captured a Wimbledon title himself, back in 2002.

Djokovic advanced in just under two hours by breaking Hewitt four times, compared to two breaks for the Aussie loser.

The 25-year-old Djokovic, a bronze medalist in Beijing four years ago, will battle fifth-seeded marathon man Jo-Wilfried Tsonga in the quarters.

One day after outlasting Canadian Milos Raonic in the longest-ever Olympic tennis match, the fifth-seeded Frenchman Tsonga had an easier time of it in a 7-6 (7-5), 6-4 victory over Spanish left-hander Feliciano Lopez on Wednesday.

Tsonga got past Raonic in an epic 48-game third set here on Tuesday.

Meanwhile, eighth-seeded Argentine slugger Juan Martin del Potro defeated 12th-seeded Frenchman Gilles Simon 6-1, 4-6, 6-3 and 11th-seeded Spaniard Nicolas Almagro handled Belgian Steve Darcis 7-5, 6-3. Del Potro captured a U.S. Open title in 2009 by stunning Federer in the final in New York.