Regis Laconi claimed his first win at Imola

Both races saw high-profile casualties, with 1996 world champion Tory Corser also thrown off his Aprilia after losing control on a corner in the second race.

The Australian's slip forced last year's world champion Colin Edwards into the gravel, and he too was forced to retire.

But neither rider had looked likely to challenge the leading pair of Xaus and Laconi, who dominated the day's racing.

It was Laconi on the Aprilia who made the best start to race one, leading for most of the 21-lap race before Xaus passed him at the Acque Minerali corner with three laps left.

Laconi then came under pressure from Bayliss and the pair went off on the penultimate lap, although the Frenchman said there was no collision.

"I simply could not avoid him after he skidded on the track," said Laconi. "It spoiled my chances of victory."

Xaus went on to finish 3.6 seconds ahead of Corser, with Edwards third on a Honda and his compatriot Ben Bostrom fourth.

Ruben Xaus was top scorer at Imola

Laconi was again the quickest away in the second race and was trailed by Edwards on the Castrol Honda.

Xaus made a slow start but nobody on the circuit could match his aggression.

He was quickly into the lead and apparently on his way to a double victory, but Laconi refused to be intimidated by the Spaniard.

The pair swapped positions several times before the Frenchman made the decisive move six laps from the end.

A slip on the final corner almost let Xaus back in, but Laconi held on to take his maiden win by less than a bike's length.

The retirement of Corser and Edwards allowed Japan's Tadayuki Okada to take third after he hauled in the leaders with a series of flying laps.

Leading results from the 13th and final World Superbike Championship race at Imola:

Race one

1. Ruben Xaus (Spain) Ducati 38 minutes 42.598 seconds
2. Troy Corser (Australia) Aprilia 38:46.199
3. Colin Edwards (United States) Honda 38:46.677
4. Ben Bostrom (United States) Honda 38:48.938
5. Tadayuki Okada (Japan) Honda 38:56.335
6. Steve Martin (Australia) Ducati 39:04.019
7. Gregorio Lavilla (Spain) Kawasaki 39:06.698
8. Stephane Chambon (France) Suzuki 39:06.878
9. Lucio Pedercini (Italy) Ducati 39:29.135
10. Neil Hodgson (Great Britain) Ducati 39:31.676