The left-hander gave up two runs on five hits, while striking out five batters as the Blue Jays defeated the Philadelphia Phillies 6-2 to complete a three-game sweep of the interleague series.
Cecil, who was recalled from triple-A Las Vegas earlier the week, admitted to feeling jitters in his first start with Toronto in 2012.
"I couldn't really calm myself down," Cecil said of the first inning. "I guess I should have pitched that way the whole game. It was my cleanest inning."
Colby Rasmus went 3-for-4 with a homer and three RBIs as Toronto completed its first home sweep in interleague play since a series with Colorado in 2007.
Jim Thome and John Mayberry hit solo home runs off Cecil (1-0) for Philadelphia (31-37).
"The first-inning jitters, first-game jitters are out of the way and now I'm just looking to build off of this one," said Cecil.
The 25-year-old was a dismal 4-11 with the Jays in 2011 but showed up to spring training in better shape and a renewed commitment. Although it wasn't enough to make the big club, Jays manager John Farrell was happy with what he saw on Sunday.
"He pitched with a lot more crispness than we last saw in spring training," said Farrell, who lost starters Brandon Morrow, Kyle Drabek and Drew Hutchison to injury in the space of five days this week. "He kept the game under control, he threw a lot of strikes and it was an encouraging outing for him."
The Blue Jays (34-32) scored six runs (five earned) on eight hits against Phillies right-hander Kyle Kendrick (2-7) over 6 1-3 innings.
Attendance at Rogers Centre was a sell out of 45,060 on Father's Day, with many of the Blue Jays' dads watching from the stands. Ricky Romero's father threw out the first pitch.
Rasmus was among the players whose father was at the game.
"It was important to me," Rasmus said "It's always good having your dad in town and to have him here on Father's Day is a great thing."
Cecil was replaced in the sixth by left-hander Luis Perez, who allowed one hit over three innings. Jason Frasor worked the ninth, allowing two hits.
Toronto scored twice in the first when Brett Lawrie and Rasmus started the inning with back-to-back doubles.
Jose Bautista walked but was picked off first by catcher Carlos Ruiz. Kelly Johnson hit a two-out single to score Rasmus.
Thome led off the second with his fourth home run of the season, his 100th for the Phillies and the 608th for his career. He also hit at least 100 home runs with Cleveland the Chicago White Sox.
"It is special because I think you look at Philadelphia, you look at Chicago, you look at Cleveland — all great baseball cities," Thome said. "To do that with the Phillies is special, no doubt. I think it's something to be proud of — you just wish you could have won the ball game with it. But it definitely is special for sure."
Mayberry led off the third with his fifth homer of the season to tie the game 2-2.
The Blue Jays regained the lead in the fourth. Yunel Escobar singled with two out, Yan Gomes was hit by a pitch and Rajai Davis bounced a single up the middle to make the score 3-2.
Rasmus hit his 10th home run of the season on the first pitch after Lawrie walked to open the fifth to stretch Toronto's lead to 5-2.
In 16 games in the second spot, Rasmus is batting .356 (26-for-73) with seven home runs, five doubles and 18 RBIs.
"I hoped I would get back to being myself," Rasmus said, "Driving the baseball and having fun and taking that approach up there against those pitchers and be able to battle them with what I think I can do."
The Blue Jays tacked on an unearned run in the seventh when Jeff Mathis led off with a double. After Lawrie lined out to right, left-hander Jake Diekman replaced Kendrick.
Rasmus greeted him with a single to right. Mathis went to third, hesitated, then ran home when right-fielder Hunter Pence bobbled the ball for an error.
"I feel like I pitched a lot better than my numbers show but it's the way this game goes," said Kendrick. "A couple mistakes here they hit. It's a pretty good hitting team over there — got to give them some credit."
Notes: Toronto is 6-6 against the National League this season. ... Jays right-hander Jesse Chavez is a leading candidate to start Tuesday in Milwaukee. He is 7-2 with a 3.84 earned-run average in 12 starts for triple-A Las Vegas. ... Thome is the fourth player to have 100 or more home runs with three different clubs, joining Alex Rodriguez, Reggie Jackson and Darrell Evans. ... Ruiz was back behind the plate for the Phillies on Sunday. He missed Saturday's game with a strained oblique muscle that forced him from Friday's game. ... Henderson Alvarez (3-6, 3.87 ERA) is scheduled to face left-hander Randy Wolf (2-5, 5.06 ERA) on Monday in the opener of a three-game series in Milwaukee.