Simona Halep's hold on the No. 1 ranking received a boost when American opponent Madison Keys withdrew from their third-round match at the Italian Open on Thursday due to a right rib injury. Halep needed to reach the quarterfinals and progress further than No. 2 Caroline Wozniacki to hold onto the top spot, and she accomplished the first task.
Wozniacki was facing 15th-seeded Anastasija Sevastova in a late match on the red clay of the Foro Italico. Keys also withdrew from the doubles competition, where she was partnered with Venus Williams.
Last year in Rome, Halep rolled her ankle in the final and lost a lead and the championship to Elina Svitolina.
Halep will next play either U.S. Open champion Sloane Stephens or seventh-seeded Caroline Garcia.
Svitolina also reached the quarterfinals, overcoming a poor start to beat 14th-seeded Daria Kasatkina 0-6, 6-3, 6-2. She'll next face either former No. 1 Angelique Kerber or Maria Sakkari of Greece.
This is the last major warmup for the French Open, which starts in 10 days.
Jelena Ostapenko, who is preparing to defend her title at Roland Garros, rallied past Johanna Konta 2-6, 6-3, 6-4 and will meet either three-time Rome champion Maria Sharapova or Daria Gavrilova.
In men's action, Fabio Fognini beat Peter Gojowczyk 6-4, 6-4 to reach his first quarterfinal in 11 appearances at his home tournament.
The temperamental Fognini slammed his racket midway through the second set and received a warning from the chair umpire but otherwise held his composure to follow up an impressive win over Dominic Thiem a day earlier.
Fognini's next opponent will be either seven-time Rome champion Rafael Nadal or Canadian teenager Denis Shapovalov.