Naomi Osaka's lead in the rankings remains in peril, although reigning French Open champion Simona Halep dropped down to third.
Nadal remains second in the rankings, a long way adrift of Novak Djokovic, with the pair facing a possible final clash at Roland Garros in three weeks' time.
World number one Djokovic, winner at the Madrid Open last week, produced an error-strewn performance in his 54th meeting with second-ranked Nadal, who claimed the 81st title of his career.
A break in each set was enough for former world number one Pliskova to get past Konta, sealing victory on her third match point after 85 minutes on court.
World number one Djokovic, the winner at the Madrid Open last weekend, defeated Argentina's Diego Schwartzman in the semifinal.
The eight-time Rome winner had been stunned by Tsitsipas, seeded eighth, in the semi-finals at the Madrid Open last weekend.
The Briton next meets either Czech fourth seed Karolina Pliskova or Greek qualifier Maria Sakkari.
The 34-year-old said he had not recovered from the injury he suffered at the Miami Masters in March where he finished runner-up to Roger Federer.
Eight-time champion Nadal will take on Greek rising star Stefanos Tsitsipas for a place in the final.
The Swiss 20-time Grand Slam winner was playing in Rome to prepare for his return to the French Open for the first time since 2015.
The Japanese star was due to meet Madrid Open champion and sixth seed Kiki Bertens for a place in the final four in Rome.
Kyrgios grabbed the headlines when he suffered a spectacular meltdown on Court Three against Norwegian qualifier Casper Ruud.
The controversial figure kicked a water bottle, threw a chair, packed his bag and stormed off court after the referee gave a point against him for unsportsmanlike conduct for swearing.
Thiem blasted tournament organisers for keeping competitors hanging around all day when play was washed out.
Sharapova, 32, a five-time Grand Slam champion, has not played since pulling out of a tournament in her native Russia at the end of January.