Romero, who batted .230 with a homer and 12 RBIs in 78 games during his first taste of Major League action with Arizona last season, walked and scored during a three-run first inning for the Tigres.
The 25-year-old Venezuelan singled in the sixth and led off the eighth with a base hit to left field before coming home on a throwing error by Astros reliever Carlos Hernandez (1-1) to snap a 6-6 tie.
Romero provided some breathing room with a two-run double in the ninth before scoring on former Pacific Coast League All-Star Rene Reyes' single as Aragua bounced back from a 3-2 loss in Game 5 on Wednesday.
Raul Chavez (Blue Jays) and Reyes finished with two RBIs apiece and Luis Maza (Dodgers) and former Major Leaguer Alex Delgado each collected three hits and drove in a run for the Tigres.
Former Orioles farmhand Victor Moreno (2-0) allowed one hit over two scoreless innings to pick up the win in relief. Yorman Bazardo (Phillies) struck out three over 2 2/3 scoreless frames after Aragua starter Heath Totten (Twins) surrendered six runs -- five earned -- on six hits and a walk with one strikeout over 3 1/3 innings.
Venezuelan League Most Valuable Player Jesus Guzman (Giants) went 2-for-4 with a three-run homer and Jackson Melian (Tigers) and Jose Castillo (Nationals) also went deep for the Leones.
Hernandez gave up an unearned run on one hit and a walk with one strikeout in one inning.
Game 7 is Friday at Caracas.