Bassitt allowed just three hits and a walk as the Blue Jays took the rubber game of the three-game series at Rogers Centre. He had three strikeouts over the 110-pitch outing.
Right-hander Jay Jackson recorded the final three outs.
Toronto (73-61) entered play 3 1/2 games out of a playoff spot in the American League.
It was Toronto's 13th shutout win of the season. The Blue Jays improved their interleague record this year to an MLB-best 28-15.
Toronto was aggressive from the outset in the mid-afternoon matchup and it paid off with an early lead.
Kirk doubled again in the fourth as the Blue Jays put up two more runs.
Bassitt (13-7), who entered with losses in four of his last six decisions, held the Nationals to two singles over the first four frames.
He gave up a two-out double to Jacob Young in the fifth but picked him off to erase the threat.
Bassitt leads the major leagues with eight starts of at least six scoreless innings. Roger Clemens set the team record of nine in 1997.
Toronto piled on in the sixth inning by recording four straight hits that pushed two more runs across.
Kirk started the rally with a single and later scored on a Clement single. Daulton Varsho scored on an Espinal single to make it 6-0.
Corbin allowed six earned runs and 10 hits over five innings. He walked a batter and had five strikeouts.
Kirk added another RBI with a sacrifice fly in the seventh that brought home Schneider.
Announced attendance was 39,303 and the game took two hours 23 minutes to play.
Toronto's Brandon Belt was still nursing a minor back issue Wednesday that prevented him from a potential pinch-hitting assignment a night earlier.
Belt was getting loose late in Tuesday's game when back spasms left him unavailable.
Manager John Schneider said Belt was "feeling a little bit better" for the series finale but he was not in the starting lineup.
Recent Triple-A call-up Mason McCoy made his big-league debut for Toronto in the eighth inning.
He came on as a pinch-hitter for Clement and struck out in his lone plate appearance.
The Blue Jays are off Thursday. Toronto will kick off a six-game road trip against the Colorado Rockies on Friday night.
The Nationals will return home for a four-game series against the Miami Marlins starting Thursday evening.
This report by The Canadian Press was first published Aug. 30, 2023.
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Gregory Strong, The Canadian Press