Serena Williams remains firmly on course for a fourth Internazionali d'Italia title after a 6-4 6-1 semi-final victory over Irina-Camelia Begu in Rome.

Playing in just her fourth tournament of the year due to illness and injury, the world number one looked laboured at times in the first set, but hit her stride in the second to power past her Romanian opponent.

The result set up an all-American final between Williams and Madison Keys, who defeated Garbine Muguruza 7-6 (7-5) 6-4 in the other semi-final.

Begu, meanwhile, earned a guaranteed top-32 seeding at next week's French Open and boosted her world ranking from 35 to 28 off the back of an impressive tournament performance.

The 25-year-old claimed the scalp of fourth seed Victoria Azarenka and did not drop a set en route to her last-four meeting with Williams.

And she certainly stretched the American during a hard-fought first set, impressing particularly with the power of her returns.

Begu looked set to launch a comeback when she broke Williams in the first game of the second set, but instead the reigning champion broke back immediately before seizing control and accelerating away to record the straight-sets win.

She will be strongly backed to claim her fourth Internazionali d'Italia title at the expense of world number 24 Keys, having defeated her compatriot in both of their previous meetings.