Serena through to last eight

Serena Williams eased into the last eight of the US Open with a 6-3 6-3 victory over Kaia Kanepi.

The top seed in New York reached the 38th Grand Slam quarter-final but surprisingly her first of 2014 as she overpowered her opponent from Estonia after 65 minutes on court.

Williams has looked totally focused on the job in hand this tournament and did not lose a point in her first three service games of the match.

Kanepi, a big hitter herself, stood toe-to-toe with her rival but once Williams made the breakthrough for 5-3, the first set was gone.

The American then managed to break again at the start of the second, though there was an embarrassing moment for the two-time defending champion when she completely fluffed a smash and dropped her serve to love.

She was also broken when serving for the match in the eighth game, though it proved to only be a temporary setback for the two-time champion.

Williams instead clinched victory on Kanepi's serve, setting up a clash with 11th seed Flavia Pennetta in the next round.

"She hits the ball incredibly hard and moves the ball around," the world no 1 said afterwards to the crowd watching on in Arthur Ashe Stadium. "I just keep fighting."

"I finally made a quarter-final this year! Glad to do it in New York."

Pennetta continued to show a liking for Flushing Meadows, reaching the quarter-finals at the venue for a fifth time in her career with a 7-5 6-2 victory over Casey Dellacqua.

The Italian has lost all five previous matches against her fellow 32-year-old Williams but will head into the clash with a positive attitude.

She said: "You just have to play your tennis and do your best. Of course, she's better than me, but if I believe I can beat her, maybe if she doesn't have a good day I can do that.

"If I get on the court and just play and try not to lose 6-0 6-0, I'm going to lose 6-0 6-0."

Russian Ekaterina Makarova moved into the quarter-finals after beating seventh seed Eugenie Bouchard 7-6(2) 6-4 as the Canadian wilted under the punishing conditions.

With stifling humidity and on court temperatures hovering near 38 Celsius (100 degrees Fahrenheit) it was another day of survival of the fittest at the year's final grand slam and it was a challenge the Wimbledon finalist could not meet, her bid for a fourth consecutive grand slam semi-final appearance coming to an end.

Bouchard's loss means that for the first time since 1977, eight women will have filled the eight finalist slots at a season's major tournaments.

Victoria Azarenka stayed on course for a third consecutive final appearance with a battling win over qualifier Aleksandra Krunic.

The 21-year-old Serbian has been one of the stars of the tournament, beating both Madison Keys and Petra Kvitova, and for a long time it looked like she might add another huge scalp.

The diminutive Krunic embraced her debut on Arthur Ashe Stadium and was an instant crowd favourite, wowing the fans with her court coverage and powerful hitting.

She won the first set and caused problems for Azarenka throughout but it was the 16th seed who came through 4-6 6-4 6-4 after two hours and 19 minutes to set up a last-eight clash with Makarova.

Azarenka, who has struggled with injury this season, said: "Alexandra played some amazing tennis. She has a great future.

"It's never easy to play somebody you don't know . She stepped it up and I just tried to stay positive and fight and do anything I could to turn the match around."