Ana Ivanovic reached her first grand slam quarter-final since winning the French Open in 2008 with a straight-sets victory over Tsvetana Pironkova at the US Open on Monday.
The Serb was expected to remain at the top of the game for many years after her triumph at Roland Garros but instead injuries and a crisis of confidence sent her tumbling back down the rankings.
She has been close to the last eight at a number of tournaments since without getting there but this time there was no stopping Ivanovic as she clinched a 6-0 6-4 win in an hour and 11 minutes.
Ivanovic will now meet Serena Williams, who she has never taken a set off in three previous meetings, including in the fourth round here last year.
Williams sent an ominous warning to Ivanovic with a 'double bagel' victory over Andrea Hlavackova.
Italy's 10th seed Sara Errani continued her annus mirabilis by knocking out sixth seed and last year's semi-finalist Angelique Kerber.
Errani had never been beyond the third round at a grand slam before reaching the quarter-finals at the Australian Open and she then embarked on a brilliant run through to the final at the French Open before losing to Maria Sharapova.
This was her first appearance in the fourth round at Flushing Meadows and she went in as the underdog but came out a delighted 7-6 (7/5) 6-3 winner.
In the last eight, Errani will play her doubles partner and fellow Italian Roberta Vinci, who stunned second seed Agnieszka Radwanska 6-1 6-4.
The 29-year-old is also having the season of her life and reached the fourth round of a grand slam in singles for the first time at Wimbledon two months ago, while she and Errani won the doubles title at the French Open.