SAN DIEGO — The Giants were already clinging to their paper thin playoff hopes when they flew south to San Diego for a four-game series against the Padres. As things stand, San Francisco will spend the next five weeks playing out the string.

With a sloppy 8-4 loss on Thursday at Petco Park, the Giants have lost 10 of their last 12 games. They’re 61-67, a season-low six games below .500, and will now fly to Milwaukee for three games against the Brewers — the best team in baseball.

And to top it off, right-hander Landen Roupp may be done for the season after sustaining an ugly left knee sprain on Wednesday.

Through three innings Thursday, the Giants owned a 2-0 lead and positioned themselves to at least salvage a series split. Justin Verlander retired the first nine batters he faced, and the offense scored a pair of runs in the third thanks to rare shoddy defense from Platinum Glover Fernando Tatis Jr.

San Diego tied the game at two apiece in the fourth, then landed its haymaker by taking advantage of San Francisco’s uncrisp defense to plate six runs and take an 8-2 lead.

With runners on first and second and no outs, the Padres’ Freddy Fermin laid down an excellent bunt to the infield’s left field. Third baseman Casey Schmitt barehanded the ball and fired to first, but the throw sailed wide and allowed a run to score.

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Jake Cronenworth, the runner on first, planned on stopping at third. That changed when right fielder Luis Matos failed to cleanly gathered the ball, giving Cronenworth a window to waltz home.

One of San Francisco’s lone bright spots on Thursday afternoon was rookie right-hander Joel Peguero. Along with throwing two scoreless innings in his debut, Peguero touched 102.1 mph on a sinker to usurp Jordan Hicks for the hardest-thrown pitch by a Giant this season.