SEGUIN — The San Diego Lady Vaqueros suffered their first loss of the postseason Thursday night.

The 5-1 setback came against what amounts to their toughest opponent of the season — Class 3A’s No. 3-ranked Hallettsville. The Lady Brahmas defeated San Diego in Game 1 of their best-of-three playoff series at Ed Kruse Stadium at Texas Lutheran University in Sequin.

The Lady Vaqueros came into the Class 3A regional semifinal match-up with a win streak which went back to the regular season. San Diego lost only one district game against rival Santa Gertrudis and then followed the regular season with six-straight playoff wins to take three playoff championships.

Maybe it was nerves, but the Lady Vaqueros committed three errors in the game.

San Diego ace Kayla Oliveira went six innings. She allowed seven hits and two walks while striking out six batters.

The Lady Vaqueros were trailing 2-1 in the bottom of the fifth when the Lady Brahmas put together a three-run rally fueled by back-to-back base hits, a sacrifice and a rare San Diego infield error.

San Diego was unable to recover.

Zalayna Perez, Leandra Bazan, Brianna Munoz and Oliveira each had a hit in the game.

The Lady Vaqueros began the game with a run in the top of the first inning. Perez led off with a single and later scored on a Cierra Perez sacrifice.

Game 2 of the series in at 6 p.m. Saturday back in Sequin. If needed, Game 3 will follow.