Novak Djokovic made it 39 matches unbeaten with a straight-sets victory over Rafael Nadal at the Internazionali BNL d'Italia.
Serbian Djokovic has not lost in 37 matches this season and claimed his seventh title of 2011 by beating world number one Nadal 6-4 6-4 in the final of the ATP 1000 event at Rome's Foro Italico.
Spaniard Nadal, a nine-time slam winner, has now lost four finals this year to the seemingly unbeatable Djokovic after earlier defeats at Indian Wells, Miami and Madrid.
It is also the first time in his career that Nadal has lost twice on clay in one season, just a week before the French Open begins on the same surface at Roland Garros.
Nadal, 24, battled valiantly to retain his title, saving seven break points but losing his serve four times over the course of two hours and 12 minutes.
Djokovic was broken twice, but only gave up three break-point opportunities and successfully defended the other.
He is now just five matches behind John McEnroe's record 42-0 start to the 1984 season and seven behind Guillermo Vilas' all-time run of 46 matches unbeaten in 1977.
Djokovic had to contend with a quick turnaround after his semi-final victory over Andy Murray, which finished past 11.30pm local time on Saturday.
After collecting the first set with a backhand cross-court winner, Djokovic began to feel the strain in the second and was forced to stretch aching muscles between nearly every point.
The pair continued to exchange heavy groundstrokes from the back of court, with little to separate them.
Eventually, an opening did appear.
Djovkovic found himself 5-4 ahead and then went 40-0 up on the Nadal serve.
Still the defending champion did not submit.
He fought hard and saved championship points, but Djokovic took advantage of a net cord to smash a final forehand winner, before slumping to the ground in celebration.