Serena Williams overcame a first-set scare to beat fellow American Christina McHale 7-6 (9/7) 6-1 to secure a quarter-final clash with Svetlana Kuznetsova at the Internazionali BNL d'Italia in Rome.
World number one Williams was down by an early break and saved a set point in the opener before breaking McHale's resolve in the second set.
McHale served for the first set in the ninth game after converting her eighth break point at 2-2, but Williams broke back to level the match.
In the tie-break McHale saved two set points before 21-time grand slam champion Williams clinched the 16th point to take the set.
Williams, three-time champion in Rome, found more consistency in the second set and broke McHale three times, sealing victory in one hour and 61 minutes on her second match point.
Russia's Kuznetsova, the last woman to beat Williams - in the round of 16 in Miami, edged a see-saw battle against Daria Gavrilova 6-2 2-6 6-3.
Kuznetsova was under pressure for much of the last two sets but made the decisive break against an increasingly nervous opponent in the eighth game of the decider.
Britain's Johanna Konta suffered a disappointing defeat to Japan's Misaki Doi, failing to follow up her win over seventh seed Roberta Vinci in the previous round to lose 4-6 7-5 6-2.
Konta began well and, after winning the opening three games, held off a Doi comeback to win the first set.
She then fought back from two breaks down to draw level in the second at 5-5 but from there lost eight of the last 10 games as Doi, ranked 45 to Konta's 23, clinched victory in two hours and 21 minutes.
Third seed Garbine Muguruza became the first player into the last eight when she turned in a clinical display to beat Latvia's Jelena Ostapenko 6-1 6-4 to set up a clash with Swiss Timea Bacsinszky.
Bacsinszky came out on top in a tough three-set battle with Spain's Carla Suarez Navarro, turning her fortunes round after coming within two points of losing the match to win 5-7 7-5 6-2.
Romanian Irina-Camelia Begu earned her place in the last eight with a 6-1 6-4 win against Russian teenager Daria Kasatkina and unseeded American Madison Keys defeated Hungarian Timea Babos 7-6 (6/2) 6-3.
Source: PA
