Triple World Superbike champion Jonathan Rea had to settle for second place in race two in Aragon as Chaz Davies secured a narrow victory.
Northern Ireland rider Rea won Saturday's opener and he moved in front after Xavi Fores slipped off.
Davies pressed Rea and took the lead with five laps left and held on to win with Marco Melandri in third.
Rea's lead at the top is cut to 12 points with Davies replacing Melandri in second place.
Alex Lowes came in a distant fourth and he was followed in by Michael van der Mark and Tom Sykes.
Melandri held the early lead before Fores powered through and the Spaniard was holding off the challenge of Rea when he slid out of the race with 11 laps remaining.
It allowed Rea to lead on his Kawasaki but he was soon under pressure from Ducati pair Davies and Melandri as the trio pulled clear.
Davies edged in front and when Rea went wide on the last lap his victory, by 1.184 seconds, was assured in the Spanish sunshine.
"It was great fun and I'm really happy - it was a good scrap with Johnny," said Davies.
Rea remains three short of Englishman Carl Fogarty's record of 56 World Superbike wins but he was content with his weekend's work.
"It was a big effort from my team and I'm happy to get a first and second," said the Ballyclare man.
|2018 WSB Riders' Championship|
|Jonathan Rea (Gbr)||Kawasaki||114 pts|
|Chaz Davies (Gbr)||Ducati||102|
|Marco Melandri (Ita)||Ducati||96|
|Xavi Fores (Sp)||Ducati||76|
|Alex Lowes (Gbr)||Yamaha||70|
|Michael van der Mark (Ned)||Yamaha||67|