New York - Three-time champion Serena Williams went level with sister Venus on 61 US Open career wins when she coasted into the fourth round on Saturday.
Olympic and Wimbledon champion Williams won eight games in succession to claim a 6-4, 6-0 win over Russia's world 42 Ekaterina Makarova, the woman who knocked her out of the Australian Open this year.
Williams, the fourth seed, fired 31 winners and eight aces and will next face either Maria Kirilenko of Russia, the 14th seed, or unseeded Czech Andrea Hlavackova for a place in the quarter-finals.
"After 4-4, I started to play better and more consistent. She's a good opponent, she beat me in Australia so I knew I needed to play better and I did," said the 1999, 2002 and 2008 winner.
Williams now has a 61-9 career record in New York with sister Venus, who was knocked out in the second round, on 61-11.
Williams will turn 31 next month, but has no intention of joining Kim Clijsters and Andy Roddick in retirement.
"I can't leave you guys. I love this sport way too much. I need to stay here for tennis," she said.
Polish second seed and Wimbledon runner-up Agnieszka Radwanska matched her best US Open performance by also reaching the fourth round with a 6-3, 7-5 win over error-plagued Jelena Jankovic.
Radwanska recorded her 51st victory of the year as she and the 30th-ranked Serb, a former world number one and 2008 finalist, toiled in 32-degree Celsius heat.
"It's always tough and tight when we play. But I prepared well and I am happy to come through in straight sets," said Radwanska, who goes on to face Italian 20th seed Roberta Vinci for a place in the quarter-finals.
Vinci reached the last 16 for the first time with a 6-2, 7-5 win over Slovakia's 13th seed Dominika Cibulkova, a quarter-finalist in 2010.
Radwanska triumphed in a gruelling 98-minute contest which featured 10 breaks of serve, with Jankovic finally undone by her 37 unforced errors, the last of which came on match point with a wild, ballooned forehand.
Radwanska again played with heavy strapping on her right shoulder but insisted she was not hurt.
"The shoulder is quite good, no complaints. I have played three very good matches here," said the 23-year-old.
Vinci equalled her best Grand Slam performance with a fourth successive victory over Cibulkova and third this year after previous wins in Indian Wells and Madrid.
The 29-year-old Italian also reached the fourth round at Wimbledon this year.
In early men's action, Spanish 11th seed Nicolas Almagro and 12th seeded Croatian Marin Cilic made the last 16.
Almagro reached the fourth round at the US Open for the first time with a 7-6 (7/3), 6-7 (4/7), 7-6 (7/2), 6-1 win over American wildcard.
Cilic, a quarter-finalist in 2009, ended Asian hopes in the singles when he ousted Japanese 17th seed Kei Nishikori 6-3, 6-4, 6-7 (3/7), 6-3.
Later Saturday, top seed Roger Federer, bidding to become the first man in 87 years to win six US Open titles, faces Spanish 25th seed Fernando Verdasco, a player he has beaten in all four previous meetings.
Britain's Olympic champion Andy Murray, the third seed, defends a 6-0 career record against Spain's Feliciano Lopez.
The two played at the US Open last year with Murray winning in straight sets.
Milos Raonic, the 15th seed, faces James Blake of the United States trying to become the first Canadian to reach the last 16 of a major for 24 years.