Jonathan Rea won race one at the World Superbike round at Laguna Seca to increase his championship lead over Alvaro Bautista who crashed early on.
Rea enjoys a 49-point advantage at the top of the standings before Sunday's sprint race and race two in California.
Rea led on every lap for a fifth race win in a row in the series and a fourth in succession at Laguna Seca as he made it a 110-point swing over Bautista.
Chaz Davies was second in Saturday's race, with Toprak Razgatlioglu third.
Kawasaki-mounted Rea secured pole position at the American circuit for the first time and produced a dominant performance to take victory by 5.6 seconds.
For the Northern Irishman, it was a 79th career World Superbike triumph in his 200th start as he followed up his triple success at Donington and race two win at Misano.
"I felt good in that race, I could have ridden the bike all day I was having so much fun. I was able to hit all my points and have to try and put on a repeat performance tomorrow," said Rea.
The four-time WSB champion now boasts five race wins at Laguna Seca, having achieved a double in 2018 and single race successes in both of the previous two years.
Rea's hat-trick in the British round had seen him assume the championship lead and he has now won eight races this season, compared to rival Bautista's 14.
The Spaniard won the first 11 races of the season to build up a 61-point lead over Rea after the sprint race at Jerez but the Ducati rider has now crashed at four consecutive rounds at the Spanish, Italian, Great Britain and United States rounds.
On this occasion the former MotoGP rider came off while lying third on lap four.
English riders Tom Sykes and Alex Lowes were fourth and fifth, with Jordi Torres completing the top six.
Eugene Laverty was 11th on his return to racing action after breaking both wrists in an accident at Imola seven weeks ago.
After Sunday's races the championship takes a summer break, with the first of the four remaining rounds taking place at Portimao in Portugal on 7 and 8 September.
|2019 WSBK Riders' Championship|
|Jonathan Rea (GB)||Kawasaki||401 pts|
|Alvaro Bautista (Spa)||Ducati||352|
|Michael van der Mark (Ned)||Yamaha||215|
|Alex Lowes (GB)||Yamaha||203|
|Leon Haslam (GB)||Kawasaki||187|
|Toprak Razgatlioglu (Tur)||Kawasaki||169|