Tanner Houck has been one of the best pitchers in the American League this season, and Saturday the Red Sox hoped to celebrate his 28th birthday by further cementing his case to start the All-Star Game while picking up another big win.

Unfortunately the Padres missed the memo, and San Diego stormed into Fenway Park to spoiled the party.

For the second straight day San Diego pounced on Boston and ran away for a rout, smashing four home runs to beat the Red Sox 11-1. The Padres once again broke the game open in the top of the fifth, scoring six runs in the frame after ambushing Boston for nine runs on Friday night, and the result from that point was never in doubt.

All told the Padres collected 16 hits as a team, the most allowed by the Red Sox in a game this season.

Houck, who came into the day with an AL-best 2.18 ERA, never seemed like himself. He allowed three straight singles in the second inning, with a run scoring on a Jarren Duran error on the third. Then he served up a two-run home run to Manny Machado in the third inning and gave up another solo shot to Jackson Merrill — the rookie’s second homer of the weekend — to lead off the fourth.

Even after that it was a manageable 4-0 deficit, but then the wheels really fell off in the top of the fifth.

San Diego batted around and had the first four men reach safely off Houck, including a leadoff walk by Luis Arraez, a single by Jurickson Profar and an RBI single by Jake Cronenworth. That brought Machado back to the plate, and the six-time All-Star smoked a slider down the middle for a three-run homer, putting the Padres up 8-0 with no outs in the inning.

Houck wound up facing one more batter, getting Donovan Solano to line out, and finished with a season-worst seven earned runs allowed over 4.1 innings on eight hits, one walk, three home runs and four strikeouts. Houck’s ERA for the season is now 2.67, dropping him from first in the league to seventh.

With Chase Anderson unavailable after pitching four scoreless innings on Friday night, Red Sox manager Alex Cora handed the ball to rookie Bailey Horn, who made his MLB debut and pitched the next 2.2 innings. Horn wasn’t perfect, allowing a two-run home run by Brett Sullivan to round out the fifth before loading the bases in the seventh, but the left-hander was able to escape that latter jam unscathed.

Merrill, a rookie standout who grew up a Red Sox fan, tacked on an RBI double against Zack Kelly in the eighth to make it 11-1. He finished 3 for 5 with two extra base hits and two RBI on the day.

Red Sox first baseman Dominic Smith pitched the ninth, becoming the second position player to pitch for Boston this season. He allowed a single in an otherwise scoreless inning, and one of his pitches was clocked at 32 mph.

Offensively the Red Sox just couldn’t get anything going, especially against Padres starter Michael King.

A former Boston College standout who starred at Bishop Hendricken in Rhode Island, King held the Red Sox to one run over six innings on five hits and a walk with six strikeouts. Boston’s only damage against the local product came on a Jarren Duran solo home run in the sixth, his eighth home run of the season.

Connor Wong also singled against King, extending his hitting streak to 15 games. According to the club he is the first Red Sox catcher to record a 15-game hit streak since Victor Martinez’s 25-game streak in 2009.

The Red Sox have now lost three straight games for the first time since dropping four straight to Tampa Bay and St. Louis from May 15-18, and this also marks the club’s first series defeat since the Red Sox lost two of three to the Orioles on May 27-29.

Boston (43-39) will look to avoid the sweep and get back on track in Sunday’s series finale, when Josh Winckowski (1-1, 3.26) takes the hill against Padres starter Matt Waldron (5-6, 3.43). Waldron is one of the sport’s last knuckleballers and was mentored by the late Tim Wakefield prior to his death.