It also might have been the most impressive.
Washington has won 11 straight against the Mariners, the longest current streak for one major league team against another.
Strasburg (11-10) went 7 2-3 innings and struck out eight, increasing his NL-best total to 210. The right-hander also broke the Nationals' single-season record of 207 set by Gio Gonzalez two years ago.
''Just the fact that he had two good ones and then a little bit of a clunker, and tonight to come back and answer, for him is important,'' Williams said. ''For him, it's just that if he throws it where he wants to, he can be dominant out there. Tonight he was really, really good.''
The right-hander's fastball sat consistently in the mid-90s (mph), but it was his changeup that befuddled the Mariners.
Seattle finally got to Strasburg in the eighth when Dustin Ackley cleared the right-field fence with his 10th home run of the season. Ackley was drafted No. 2 overall in 2009 - directly behind the Washington phenom.
Matt Thornton came on to close out the inning, and Rafael Soriano worked around two ninth-inning singles for his 30th save in 35 attempts.
''He was tough on us tonight,'' Mariners interim manager Trent Jewett said of Strasburg. ''We contributed to that some. He was good. He got the win. He deserved it.''
Werth gave the Nationals an early lead with a two-run homer in the first off Roenis Elias, who got the ball after Chris Young was pushed back to Monday. Elias (9-12) recovered to last six innings for the first time since June 28. He allowed three runs - two earned - and six hits.
Seattle threatened in the ninth when Kyle Seager and Endy Chavez singled, but Soriano retired James Jones on a game-ending grounder.
Anthony Rendon had an RBI single in the fifth for the Nationals.
Strasburg pitched out of trouble on multiple occasions. In the third, he left runners on second and third by throwing a called third strike past Robinson Cano for his first strikeout. Strasburg also stranded runners at the corners in the fifth by fanning Ackley.
Strasburg, who walked none, has allowed one run in three of his past four starts.
''I just stuck to the game plan. I just kept executing pitches,'' he said. ''Let them hit my best stuff.''
Mariners: Jewett said OF Chris Denorfia (stiff neck) is a little banged up, but was available off the bench.
Nationals: Despite hitting two home runs Friday, catcher Wilson Ramos did not start behind the plate. Williams said that was partly to lighten the workload for Ramos and limit the wear and tear on him. Ramos was the DH.
Mariners RHP Hisashi Iwakuma tries to bounce back in the series finale Sunday after allowing five runs over 2 1-3 innings at Boston in his most recent start.
Nationals RHP Tanner Roark looks to allow three runs or fewer for the fifth straight start.
Elias has allowed his fair share of baserunners, including 12 walks in his last three starts, but has been adept at finding a way out of jams. The left-hander has induced a team-leading 20 double plays, including two on Saturday.