New York - Polish second seed and Wimbledon runner-up Agnieszka Radwanska matched her best US Open performance on Saturday by 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 had also reached the fourth round at Wimbledon this year.
Former champions Roger Federer and Serena Williams complete the afternoon session on Arthur Ashe Stadium.
Top seed 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.
Fourth-seeded American Williams, the champion in 1999, 2002 and 2008, tackles Russia's Ekaterina Makarova who knocked her out of the Australian Open in the fourth round earlier this year.
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.
Blake, the world 114, is one of four wildcards who has made it to the third round, the most at any Grand Slam in the Open era.