Richard's teammates greeted him in a mass celebration on the field, as the Padres (16-26) took the Interleague set, 2-1, winning a series for the third time this season.
"Clayton was due," Padres manager Bud Black said. "Just watching Clayton in batting practice, he has the ability to launch some balls. He pinch-hit last year and got a hit.
"And he's fast. He's one of our faster pitchers. It swung to our favor if Will was going to do what he did once the count got to 3-2. He was on the move with the pitch. The ball was hit in the right area. We caught a break with the bobble."
Richard, who's scheduled to start Monday against the Cardinals in St. Louis, improved to 2-for-2 in his career as a pinch-hitter.
"It's something where you go in the game and you never know what you're going to get," Richard said. "It's definitely not something you anticipate going to the ballpark. It's a pleasant surprise."
Richard said he didn't see Kendrick bobble the ball -- he was watching third-base coach Glenn Hoffman, who waved him home.
"No slide, just straight Michigan quarterback sprinting," Black said.
Venable's second career walk-off hit sealed the Padres' first victory in four extra-inning games this season and ended a four-hour, 23-minute endeavor that included a combined 41 players, 14 pitchers and 26 stranded baserunners. Richard was the second starting pitcher called off the bench to hit -- the Angels' Dan Haren struck out in the top of the 13th.
In another odd moment, the Angels (18-24) used a five-man infield, with Kendrick coming in from left field when the Padres had a runner on third with one out in the 11th. Cameron Maybin struck out. After Kendrick returned to left field, Chase Headley grounded out to end the inning.
Kendrick's move to left field was necessary because Vernon Wells (thumb, third inning) and Ryan Langerhans (shoulder, 11th inning) suffered injuries.
Reliever Miles Mikolas (1-1) earned his first victory in his eighth Major League game, throwing two scoreless innings. The Padres kept the lineup card for him. Richard hit for Mikolas, who watched on.
"At first, I thought he would get to third, but they bobbled the ball and everyone jumped up, so I jumped up with them and tried to get on the top step and watch to see if there was going to be a play at the plate," Mikolas said. "[He] skated right in there.
"To see other pitchers out there, even when it's their off-day as a starter, they're very much in the game."
Hours earlier, Yonder Alonso's two-run double tied the game, 2-2, in the fifth. The double was his team-leading 14th of the season and his second double of the game. He has hit two doubles in a game five times this season, one game shy of the Padres' record. Tony Gwynn, in 1993, and Adrian Gonzalez, in 2007, had six games with more than one double.
Padres starter Anthony Bass, whose ERA is 2.89, allowed two runs, struck out six and walked three in six innings. Mike Trout's fourth home run, a solo shot off Bass, gave the Angels a 2-0 lead in the fifth. Mark Trumbo's RBI double put the Angels ahead, 1-0, in the first.
Angels starter Ervin Santana, whose ERA is 4.22, struck out six in six innings. He gave up two runs on six hits and two walks.
"We had some opportunities early in the game. We couldn't get it done," Angels manager Mike Scioscia said.