HOUSTON — The formula that propelled the Royals to winning four straight games entering Tuesday night disappeared in the second game of a three-game set against the Astros.

An atypical rough night from the Royals defense led to starter Brady Singer struggling through five innings, and the offense was shut out in the Royals’ 4-0 loss at Minute Maid Park, giving them their second loss in their last nine games.

Six days after holding the Astros scoreless until the seventh inning, when he allowed two runs, Singer faced trouble early and often on Tuesday. The right-hander allowed four runs (one earned) on seven hits, facing stress in all five innings and needing 104 pitches to get through the night.

Singer wasn’t helped by his defense in the first inning, when the Astros scored three unearned runs. First baseman Ryan O’Hearn — filling in for an injured Carlos Santana (hip flexor strain) — booted Jose Altuve’s leadoff grounder, which was originally called a hit but later changed to an error.

Then, O’Hearn couldn’t scoop shortstop Nicky Lopez’s throw in the dirt on Aledmys Díaz’s sharp grounder. The official scorer ruled the play as an errant throw that allowed the third run to score.

The defense put the Royals in an early hole that the offense couldn’t overcome. After knocking 13 hits on Monday and averaging more than five runs per game in their last eight games, the Royals were held to just four hits against Astros starter Luis Garcia on Tuesday.

Kansas City had a runner on third base just twice. The first came in the third, when Michael A. Taylor doubled and then executed a double steal with Jarrod Dyson, who walked. Taylor then tried to steal home against Garcia, who has a long and funky delivery, but Garcia sped up when he saw Taylor take off and threw home in time for catcher Jason Castro to tag Taylor out.

Lopez, who singled, reached third base with two outs in the fourth inning, but O’Hearn flied out to take away the momentum.