Jonathan Rea is on the verge of being the first rider to win the World Superbike Championship three years in a row by completing a double in Portugal.
The Northern Irishman has a 120-point lead with six races remaining as he bids to make history.
Rea started in ninth but moved in front on lap two won by 5.8 seconds, with Michael van der Mark second and Marco Melandri in third.
Welshman Chaz Davies was second until crashing out with three laps left.
Davies missed the chance to move second in the standings and Rea now holds a massive lead over Kawasaki team-mate Tom Sykes, who missed both races in Portugal after being injured in practice on Saturday.
Rea made a superb start and moved past Leon Camier to take a lead which was never threatened although he chalked up his 11th win of the season despite having no power in second gear for the last eight laps.
Davies was also cruising in second spot at Portimao until the late crash which leaves him 15 points behind Sykes.
Eugene Laverty came close to making it two Northern Ireland riders on the podium but he had to settle for fourth while Alex Lowes crashed on lap seven.
"I'm so happy - it is an incredible day and an incredible weekend," said Rea.
"But I was lucky to finish as I had no power in second gear after the bike cut out with eight laps left.
"Even though I had a three or four-second lead, I was working hard and I was worried I would not finish."
Race Two result (World Superbike Championship round 10, Portimao, Portugal):1 Jonathan Rea (Gbr) Kawasaki 34mins 40.917secs, 2 Michael van der Mark (Ned) Honda 34:46.751, 3 Marco Melandri (Ita) Ducati 34:50.118, 4 Eugene Laverty (Gbr) Aprilia 34:53.709, 5 Jordi Torres (Spa) BMW 34:56.860, 6 Lorenzo Savadori (Ita) Aprilia 35:00.276, 7 Leandro Mercado (Arg) Aprilia 35:04.203, 8 Anthony West (Aus) Kawasaki 35:17.899, 9 Ayrton Badovini (Ita) Kawasaki 35:29.461, 10 Takumi Takahashi (Jpn) Honda 35:30.917.
|2017 WSB Riders' Championship|
|Jonathan Rea (Gbr)||Kawasaki||431 pts|
|Tom Sykes (Gbr)||Kawasaki||311|
|Chaz Davies (Gbr)||Ducati||296|
|Marco Melandri (Ita)||Ducati||250|
|Alex Lowes (Gbr)||Yamaha||169|
|Xavi Fores (Spa)||Ducati||156|