But when Richmond meant to throw his slider down and away but left it out over the plate during a sixth-inning at-bat, Guerrero pounced, sending the pitch into the Jays' bullpen for a solo home run that put the visiting team ahead in a 7-3 Toronto loss at Rogers Centre.
Richmond, a rookie right-hander, gave up three runs in the third inning, but otherwise pitched well against a potent Angels lineup with five switch-hitters and one left-handed batter.
Adam Lind made up for the Angels' third-inning outburst with a game-tying three-run shot in the bottom of the frame, but the Jays (56-65) were unable to get much offense beyond the top three hitters in their lineup and fell to 1-4 on the homestand.
Richmond has not had the luxury of pitching on a regular five-day schedule since returning to the rotation after missing a month with a right shoulder injury. He made just his third start since July 31 on Saturday, but he pitched effectively, holding the Angels (74-47) to just three hits and two walks over six of the seven innings he pitched.
In the third, however, Richmond (6-7) gave up three doubles and a walk, allowing three runs to score before manager Cito Gaston visited the mound to try to help the right-hander get his rhythm back.
"I just wanted to talk to him about his tempo," Gaston said. "He started the game with really good rhythm and stuff, and then, when a couple of guys got on base, he slowed down a little bit. I just feel like he pitches better when he has good tempo, good rhythm. He pitched a good game for us, really."
Big innings have been the culprit in a number of Richmond's losses, and he feels deep hits to the outfield could be to blame when he loses his tempo.
"I do notice what [Gaston] says -- I work more effectively when I work quickly," Richmond said. "When I'm getting the ball back from the catcher and it's quick outs ... I'm able to get in a groove and work quicker and things start flowing nicely.
"But when they hit it around in the outfield, I've got to wait a little bit for it to get back, and it's kind of slowing me down and frustrating [me]."
Despite the big inning, Richmond finished with a line of seven innings with four runs on six hits and three walks.
"We saw video on him," Angels manager Mike Scioscia said. "You can see the stuff is there. On any statistical analysis, his stuff is good. He's one of the good young pitchers coming into the league."
Richmond struck out 10 batters -- one shy of his season high -- and he credited his slider for the swings and misses.
"It's always been a good strikeout pitch for me," Richmond said. "These guys are excellent hitters, and they love fastballs. Once I get ahead -- they've never seen me pitch live against them -- so I'm trying to show them my best pitch and hopefully they'll swing at it. [I] got a few swings today."
Two of the runs in the Angels' three-run third scored when Maicer Izturis hit a fly ball to left field that bounced off Lind's glove as the outfielder made a sliding attempt at a catch.
"I get to a lot of balls, but when it hits my glove, I expect to make the catch," Lind said. "Maybe the ground caused me to move my arm or something, but I should have caught the ball."
Lind more than made up for the play in the bottom of the frame, as the Angels' 3-0 lead evaporated with one swing of his bat. Lind clubbed his 25th home run of the season off Angels starter Ervin Santana (7-6), scoring Marco Scutaro and Aaron Hill.
With Lind's blast and Hill sitting at 29 home runs, the Blue Jays join the Twins and Rangers as the only three American League teams with two 25-homer hitters. The Jays have not accomplished that feat since 2006, when Vernon Wells hit 32 and Troy Glaus hit 38.
The score was tied until the sixth inning, when the Angels took the lead on Guerrero's solo shot.
"The Vladdy pitch was just executing sliders down and away," Richmond said. "[It was] working well until that point, and I just didn't execute one. And that's why he is who he is. He makes you pay when you miss."
Guerrero crossed the plate again in the eighth, as Juan Rivera followed his single with a two-run shot to right field off reliever Brian Tallet. That gave Los Angeles a 6-3 advantage, and the Jays were unable to come back.
With fewer off-days ahead for the Jays, Richmond likely will have a more regular pitching schedule in the future. And while the third inning was trouble for the rookie, Gaston was pleased with the way Richmond performed.
"He got in a little trouble there and gave up three runs," Gaston said. "Guerrero, he's getting him all day with a breaking ball in the dirt, and then a slider up there and he got it out of the ballpark.
"But otherwise, [Richmond] pitched good. He pitched real well for us."
Erik Gilbert is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.