(Reuters) - Swede Rikard Karlberg launched his title defense in impressive style at the Italian Open on Thursday, eagling his final hole to seize a one-shot lead over home favorite Francesco Molinari in the weather-hit opening round.

Karlberg fired a sparkling seven-under-par 64 at Golf Club Milano in Monza where almost five hours of scheduled play was wiped out by torrential rain and the threat of lightning.

More than half the field did not finish the opening round, including Masters champion Danny Willett of England and Germany's Martin Kaymer who will both represent Europe at this month's Ryder Cup, and 17 players were yet to start.

Italian Molinari recorded three birdies on each nine to card a 65 while Robert Karlsson and Spaniard Adrian Otaegui opened with matching 66s.

"That was good as it gets," Karlberg, who beat Kaymer on the second extra hole in a playoff for last year's Italian Open, told reporters. "It was a great round.

"I felt at a few tournaments there have been too many bogeys, and I haven't been able to save par to get the round going.

"But today I did that very well, and in the end I shot seven under, so I'm very happy with that."

Karlberg, 29, has posted four top-10s on the European Tour since his breakthrough victory in Italy last year, including an impressive runner-up spot at the BMW PGA Championship in May.

First-round play is scheduled to resume at 7.30 a.m. local (0530 GMT) on Friday when Willett and fellow Englishmen Matt Fitzpatrick and Andy Sullivan will hope to fine tune their preparations for the Sept. 30-Oct. 2 Ryder Cup.

(Reporting by Mark Lamport-Stokes; Editing by Pritha Sarkar)