Paxton, from Ladner, B.C., gave up nine runs — eight earned — as Toronto crushed the visiting Seattle Mariners 14-4 on Monday night.
The Blue Jays drafted Paxton in the supplemental first round of the 2009 draft with the 39th overall pick. Toronto and Paxton could not strike a deal and he was picked in the fourth round in the 2010 draft by the Mariners.
"I just didn't have a good feel for it tonight," said Paxton, who was playing against the Blue Jays for the first time. "I felt like I was all over the place. When I was in the strike zone, it was the heart of the plate and they were hitting the ball hard. I think I probably just wanted it a bit too much.
"My stuff didn't feel great tonight. I didn't have a good feel for anything."
Mariners manager Lloyd McClendon agreed, pointing to the young pitcher's nerves.
"I think he was probably a little bit too amped up," said McClendon.
Danny Valencia drove in three runs with a triple and Jose Bautista, Kevin Pillar and Anthony Gose homered as the Blue Jays nearly equalled their total of 18 runs from the 1-6 road trip that ended Sunday.
"You try to do that every night but it's not that easy," Blue Jays manager John Gibbons said. "I thought we had a real good approach at the plate and made Paxton work. We got some big hits. We haven't had a laugher in a good while. I can't remember the last time."
Paxton (6-4) did not survive the third inning, allowing seven hits and six walks in 2 2-3 innings.
Left-hander J.A. Happ (10-11) became the fifth Blue Jays starter to reach double numbers in wins this season, allowing seven hits, including a home run by Kyle Seager, and two runs over seven innings.
"It feels good to go out and get deeper in the game, accomplish some of the goals that I kind of felt I could do and wanted to have the opportunity to do," said Happ. "I haven't taken a lot of time to reflect on the year but I just want to just keep going out and kind of keep us in the game for the most part.
"Play like we play tonight and we're going to have a lot of fun."
It is the first time the Blue Jays (79-77) have had five starters win at least 10 games in one season. It is the third time they have had five pitchers with at least 10 wins when relievers are included.
The Blue Jays led 4-1 after the first inning and 9-1 after three innings to hand Seattle (83-73) its third loss in a row.
The Mariners scored a run in the first when Robinson Cano doubled home Austin Jackson led off with an infield single.
Toronto replied with four runs in their first inning on a bases-loaded triple by Valencia and a single by Steve Tolleson.
Valencia's triple was not without some controversy. He was awarded third base when a video review determined he was safe after the Blue Jays challenged the out call.
Toronto chased Paxton in the five-run third to increase their lead to 9-1. The inning included Bautista's 35th home run of the season. That moved him past George Bell and tied Joe Carter for third on the Blue Jays' all-time list with 203 homers.
Seager hit his 25th homer of the season in the sixth to cut the lead to 11-2.
Pillar hit his first homer of the season, a two-run shot, in the sixth.
Gose, who entered the game among the seventh-inning defensive changes, hit his second homer of the season in the seventh to make it 14-2 for Toronto.
Rookie Kendall Graveman allowed a run in the eighth to make it 14-3.
Toronto reliever Sean Nolin allowed a homer to Chris Denorfia in the ninth for the final score.
NOTES: RHP Chris Young will not start for the Mariners in the finale of the four-game series on Thursday after going 0-3 with an 8.25 earned-run average in his past five starts. Manager Lloyd McClendon said he is showing fatigue after coming back this season from surgery. … DH Adam Lind (sore back) was out of the Blue Jays starting lineup for the third consecutive game but should return on Tuesday. …RHP R.A. Dickey (13-12, 3.82 ERA) will start for Toronto on Tuesday against Seattle RHP Felix Hernandez (14-5, 2.07 ERA). …Announced attendance at Rogers Centre was 15,548.