But it can only continue for one more match.
Venus and Serena posted identical, 6-2, 6-1 victories in the third round Saturday. Another win, and they'll face each other in the quarterfinals.
Four of the top 10 women's seeds have lost, including No. 1 Ana Ivanovic. The sisters are the only former champs left.
Venus opened play at Arthur Ashe Stadium by beating No. 27 seed Alona Bondarenko, of Ukraine. About 5 hours later, on the same court, Serena defeated 30th-seeded Ai Sugiyama, of Japan.
The way both are playing and the way the top seeds are dropping, a repeat of their finals matchup at Wimbledon would seem quite plausible. Except for the pesky reality of being in the same part of the draw.
Serena, the No. 4 seed, has lost just 10 games in three straight-sets wins. Venus, seeded seventh, has dropped 11.
"I think that definitely the Wimbledon win helped me a lot to change my mentality, to realize not everything has to be perfect all the time," said Venus, who beat her sister in that final.
Julie Coin's magical stay at the Open is over. The world's 188th-ranked player upset Ivanovic on Thursday, but she fell in the third round, 6-4, 6-4 to fellow Frenchwoman Amelie Mauresmo, the No. 32 seed.
Venus Williams will next face No. 9 seed Agnieszka Radwanska, of Poland. Radwanska beat 18th-seeded Dominika Cibulkova, of Slovakia, 6-0, 6-3.
On the men's side, No. 1 seed Rafael Nadal came back from down a break in the second set to beat Serbian Viktor Troicki 6-4, 6-3, 6-0. His next opponent will be American Sam Querrey, who reached the fourth round of a grand slam for the first time with a 7-6 (5), 7-6 (5), 6-2 victory over No. 14 seed Ivo Karlovic, of Croatia.
The 20-year-old Querrey came into the year with two goals: to win an ATP event and raise his ranking into the 30s. He has accomplished both, winning in Las Vegas in March and climbing to No. 38 in May.
Querrey, who is 6-foot-6 and ranked 55th, is considered the tall guy with the big serve against most foes, but not the 6-10 Karlovic. In his second-round match, Karlovic led Florent Serra 42-0 in aces.
This time, Karlovic only edged Querrey 24-20.
"If I can get my racket on the ball, it's not too bad," Querrey said of Karlovic's serve. "I'm a tall guy, as well. It's up near my shoulders, where other guys, it's toward their head."