Serena Williams, Novak Djokovic advance at U.S. Open

Serena Williams, Novak Djokovic advance at U.S. Open
Serena Williams celebrates during her fourth-round win over Kaia Kanepi at the U.S. Open on Monday. (Chris Trotman / AFP/Getty Images)

Like the mailmen, Serena Williams and Novak Djokovic went about their appointed rounds with efficient delivery at the U.S. Open tennis tournament here Monday.

It was Labor Day, and many of the players, fighting through physical distress in the heat and humidity, would have agreed it had been aptly named.

Not so much Williams and Djokovic, the No. 1-seeded players in the women's and men's divisions, who certainly had to break a sweat. Both played in the worst heat of the day, but both dominated.

Williams, the last U.S. player remaining in either singles bracket, powered past Estonia’s unseeded Kaia Kanepi, ranked 50th, in a relatively uneventful 6-3, 6-3 match.

Asked about getting to the quarterfinals of a Grand Slam tournament, where she hasn't been all year, Williams replied both jokingly and sarcastically.

"I never thought it would be so exciting," she said.

Of course, with 18 Grand Slam titles and seven other major finals appearances alone, she has been in quarterfinals of these big tournaments more often than she can count. So this year was an aberation.

Djokovic dispatched Germany’s Philipp Kohlschreiber, 6-1, 7-5, 6-4, and quickly summed up the thoughts of players on this sweltering day.

"The match today," he said, "it doesn't feel that it went very easily. Obviously, I had to run. I had to run a lot."

Djokovic will next play Andy Murray in the quarterfinals. Murray has slipped to an eighth-seeded position, but Djokovic expected more than the usual No. 8.

"I think, in the big matches," he said, "as the tournament progresses, he's still fit. He still plays very high quality tennis."

Djokovic, who is attempting to make his fifth straight U.S. Open final, won in 2011 and lost in the final to Murray in 2012.

Among those hardest hit by the heat was young Eugenia Bouchard of Canada, the Wimbledon finalist, who was seeded No. 7 here and was taken out by No. 17, Ekaterina Makarova of Russia, 7-6 (2), 6-4. During the match, Bouchard, 20, had her blood pressure taken and was treated with ice by medical personnel.

In other matches, Bob and Mike Bryan, the longtime No. 1 doubles team, kept rolling toward their fifth U.S. Open title. In all, the twins from Camarillo have won six Australian Opens, two French, and three Wimbledons, to go with their U.S. Open crowns. The beat fellow U.S. players Tim Smyczek and Bradley Klahn, 6-3, 7-6 (5), and are in the quarterfinals.

The team that beat them in this year’s Wimbledon final, U.S. player Jack Sock and Canadian Vasek Pospisil, seeded eighth, took a lopsided defeat at the hands of Argentinians Leonardo Mayer and Carlos Berlocq, 6-2, 6-2.

The top-seeded junior girls player, Catherine (CiCi) Bellis of Atherton, Ca., breezed through her first match against Mexico's Renata Zarazua, 6-1, 6-3.