Novak Djokovic must return on Saturday to finish the job in his Internazionali BNL d'Italia quarter-final against Juan Martin del Potro after rain forced an early end to play on Friday.
World number two Djokovic is in the hunt for a fifth title in Rome and cruised through the first set 6-1 against the unseeded Argentine.
However, play was suspended with Del Potro 2-1 to the good in set two, neither player having managed a break.
Del Potro enjoyed success on the Djokovic serve in the first game of the match, but did not win another game in the opening set as the Serbian ruthlessly seized control.
Cagoules were the order of the day in the stands and the rain grew heavier early in the second set, as Del Potro looked like he was beginning to settle.
The weather soon became too severe for play to continue, meaning Dominic Thiem - who overcame Rafael Nadal earlier in the day - must wait to discover the identity of his semi-final opponent.