TORONTO — Clay Buchholz has enough experience with Pablo Sandoval to know not to miss on a pitch when the slugger is at the plate.

The Blue Jays right-hander did just that Wednesday, and Sandoval tagged his former Red Sox teammate with a home run to help lead the San Francisco Giants in a 4-0 win.

"I've been around Pablo for a while. He hits pitches that are not where they're supposed to be really hard," Buchholz said.

Moments after the game, which saw Toronto's offence stymied by Drew Pomeranz (1-2) and the Giants bullpen, the Blue Jays announced the promotion of the hard-hitting Vladimir Guerrero Jr.

Baseball's top prospect will join the Blue Jays Friday when they begin a three-game home series against the Oakland Athletics.

Buchholz said he was excited to see Guerrero in Toronto after the 20-year-old had spent the last few seasons mashing minor-league pitching at every level.

"I got to see a little bit of him when I was down there in Florida (while both players were rehabbing injuries after spring training). He's pretty special," Buchholz said.

Pomeranz (1-2) pitched six scoreless innings in the Giants' victory Wednesday, allowing just two hits, walking a pair and string out five to pick up his first win of the season.

Evan Longoria, Brandon Belt and Buster Posey drove in a run apiece for San Francisco (11-14).

Buchholz (0-1) took the loss, allowing four runs and six hits with two strikeouts over five-plus innings in his third start in a Toronto uniform.

"I thought Clay pitched pretty good, he gave us a chance," Blue Jays manager Charlie Montoyo said. "He threw strikes, he kept us in the game, we just didn't swing the bats today."

The Blue Jays (11-14) didn't get their first base-runner until the bottom of the fifth when Pomeranz walked Rowdy Tellez. Teoscar Hernandez followed with a single for Toronto's first hit, but he was thrown out by a laser from Gerardo Parra in left field while trying to stretch it to a double.

A double from Posey in the sixth inning cashed in Parra for the Giants' third run and took Buchholz out of the game after 70 pitches. Longoria followed with another RBI double off reliever Tim Mayza for a 4-0 lead.

Sandoval led off the fifth with a no-doubt solo shot off Buchholz to put San Francisco up 2-0. It was his second homer of the season and second of the series after also going deep Tuesday night.

Belt put the Giants on the board 1-0 in the fourth, plating Steven Duggar from second base on a two-out, ground-rule double. Duggar recorded the game's first hit when he led off the frame with a single.

Toronto's Eric Sogard recorded a single in the sixth, giving him at least one hit in seven games since he was called up from triple-A Buffalo last week.

Giants centre fielder and former Blue Jay Kevin Pillar continued to receive standing ovations from the crowd of 19,652 in his plate appearances Wednesday. Pillar was 1 for 3 with a double and an intentional walk.

Tuesday's game had marked Pillar's first in Toronto since he was traded to the Giants on April 2 and the team honoured him with a video tribute.

Toronto infielder Freddy Galvis (left hamstring tightness) had his iron-man streak snapped at 349 games. Galvis was injured Sunday against the Athletics in Oakland but had pinch hit in Tuesday night's game to keep that streak intact. Montoyo said a stint on the injured list was a possibility for Galvis, who has been one of Toronto's best hitters this season.

"After the game I went and gave him a hug," Montoyo said. "It's tough to do, 300-something games. Not many people can do that. I told him I'm proud of him and that's awesome."