Nationals starter Chien-Ming Wang (2-2) needed 95 pitches to work through five innings, allowing four hits — including a two-run homer by Jose Bautista — five walks and two runs while striking out five. He threw only 48 strikes but it was enough to earn the win.
Tyler Clippard pitched the ninth inning for his ninth save.
It was the fifth victory in a row for the National League East-leading Nationals (37-23), all against American League East teams. They swept the Boston Red Sox in a three-game series at Fenway Park before going to Toronto.
It was the fifth loss in the past six games for the Blue Jays (31-30), who will try to salvage one win from the three-game interleague series on Wednesday afternoon.
Henderson Alvarez (3-6) was again hurt by the home run ball, allowing three of them on Tuesday. He has given up 16 homers, the most on the staff, in 13 starts. The homers cost him four runs against Nationals, who reached him for nine hits in seven innings. Alvarez allowed no walks and struck out three.
The 19-year-old Harper, who had three hits in Monday's 6-3 Nationals victory, had three more on Tuesday. He powered his seventh homer of the season to centre, an impressive shot, with two out in the third to produce the first run of the game.
The Nationals added two runs on Espinosa's sixth homer of the season with two out in the fourth. It scored Adam LaRoche who led off with a double.
Bautista hit his 18th homer of the season to cut the lead to 3-2 in the fifth. It scored Brett Lawrie who led off with a walk and reached second base when Espinosa did not cleanly field a sharply hit ball by Colby Rasmus and failed to turn a double play.
The Nationals came back with another homer in the seventh, the first of Solano's major-league career with two out to bump their lead to two runs. It also was the first major-league RBI for the Colombian catcher, coming in his fourth game after being promoted from triple-A Syracuse.
Notes: Attendance at Rogers Centre was 22,538....Blue Jays pitcher Brandon Morrow will be put on the disabled list on Wednesday after coming out of his start in the first inning on Monday with a strained left oblique ....Yan Gomes was returned to Class AAA Las Vegas before Tuesday’s game. ...Left-handers Aaron Laffey and Evan Crawford were called up after Monday’s 6-3 loss to Washington and Chad Beck was demoted. ...Bautista walked in his first two plate appearances on Tuesday and has reached base in 13 consecutive games and in 18 of his past 19 games. ....Toronto will start Kyle Drabek (4-6, 4.43 earned-run average in Wednesday afternoon’s series finale against Stephen Strasburg (7-1, 2.41 ERA).