As the remaining pack bore down on him, Xaus lasted as long as the end of lap 19 before eventually pitting and dropping to the bottom end of the top ten. A drive-through penalty, however, would see him cross the line in 14th position.
Victory was Spies' though, the American cruising across the line to continue in his quest to close the gap on Haga, who otherwise managed to battle his way up to fifth position – passing Yukio Kagayama on the final lap – having run as low as 19th at one stage. The gap between the two riders in the standings is now down to 39 points.
Although disappointed to miss out on winning, Byrne held off Fabrizio and a charging Smrz, who was the fastest rider in the latter stages, to finish as the best Ducati on home ground in second - easily his best result on the Sterilgarda Ducati.
Behind Haga, Kagayama defied his injury woes to finish a heroic sixth, ahead of Rea, who deserves plaudits for producing a good result despite his various problems throughout the race.
Tom Sykes prevailed in a lengthy battle with Nakano to finish eighth, with the Japanese rider finishing well up on team-mate Max Biaggi in ninth. Matthieu Lagrive rounded out the top ten on his WSBK debut aboard the Althea Honda.
Checa recovered to a frustrated 11th, ahead of Haslam, who left it too late to pit, while Biaggi, Xaus and Alessandro Polita, on his return, completed the points paying positions.