Rafael Nadal came out firing after a lengthy rain delay to beat Alexander Zverev in an enthralling Internazionali d'Italia final and return to the top of the rankings.

Zverev was on course to beat the 16-time grand slam champion for the first time when he led 3-1 in the final set, but Nadal won four games in a row following a break of around 50 minutes to turn it around.

Nadal bossed the opening set, but was outplayed in the second and up against it in the decider before regrouping to claim a record eighth title in Rome, beating the defending champion 6-1 1-6 6-3.

The top seed will replace Roger Federer as world number one and heads into the French Open having won three of the four events he has entered on clay since returning from injury.

Defeat for Zverev ends a 13-match winning streak, which earned him back-to-back titles in Munich and Madrid, but it may have been different story if the rain had stayed away at such a crucial stage at the Foro Italico.

Zverev made an ideal start, breaking in the opening game of the match when Nadal ended an enthralling quality rally by drilling a backhand long but the Spaniard hit straight back to level with a deft drop shot on the run.

Nadal took complete control of the opening set, pummelling Zverev with brutal groundstrokes from the back of the court, a blistering forehand flashing past the flat-footed youngster to leave him 3-1 down following another exquisite rally.

A flustered Zverev tossed his racquet down towards his chair after failing to put a forehand away and Nadal was pumping his feet to celebrate taking a 5-1 lead, having conjured up a classy stop volley at full stretch and unleashing a fierce forehand winner down the line.

Nadal wrapped up the set in just over half an hour, but Zverev dusted himself down to turn the tide in spectacular fashion with storm clouds gathering in the Eternal City. 

The 21-year-old stopped the rot with a hold in the opening game and all of a sudden he was toying with Nadal, breaking with a vicious forehand winner that the top seed could only thud into the net. 

Zverev was on a roll, moving the 'King of Clay' from side to side before a rasping forehand put him 4-0 up and he took it into a decider with a brilliant backhand winner, Nadal coming up with just one winner in the second set.

Incredible athleticism from Nadal saved a break point with a stunning backhand volley at the net but he missed another smash to lose a lengthy first game of the second set and go a break down.

Rain halted Zverev's momentum when he led 3-1 and it was Nadal who came out firing following a lengthier delay at 3-2, the favourite breaking straight after the restart with his opponent looking a little flat.

Nadal had the wind in his sails and a startled Zverev was on the ropes after landing a lob just beyond the baseline to go 5-3 down and the legendary left hander regained his title in style with a backhand stop volley.