Romero (13-4) struck out seven, walked two, and only got into trouble once.
The Titans have gotten complete games in their first two games at the CWS. Jason Windsor pitched a three-hitter in a 2-0 win over South Carolina on Saturday.
In the earlier game Monday, South Carolina eliminated LSU with a 15-4 victory and will face Miami on Tuesday. The loser of that game will be knocked out of the CWS. The winner will play Fullerton on Wednesday.
Cal State Fullerton (44-21) has won seven straight and 29 of 34 games. The Hurricanes (50-12) saw their 13-game winning streak end.
Miami's J.D. Cockroft (9-5) struggled for the second year in a row in the CWS. He lasted only 3 2-3 innings - his shortest outing in 12 starts - and gave up nine hits and five runs. He was hurt by four Miami errors.
In a 13-2 loss to Texas last year, he allowed 10 hits and 10 runs and his teammates committed five errors in 3 1-3 innings.
Kevin Melillo had four hits and was ejected and reinstated after a collision at home plate, leading South Carolina over LSU.
The Gamecocks trailed 3-1 before they scored six runs, four unearned, with two outs in the sixth.
South Carolina had the bases loaded with two outs when Nick Gardiner singled to right off Lane Mestepey (7-4). Landon Powell scored easily, but Melillo collided with LSU catcher Matt Liuzza after the ball bounced under Liuzza's glove.
Umpire Bob Homolka called Melillo safe, but immediately ejected him for not trying to avoid the collision.
South Carolina coach Ray Tanner came out of the dugout to protest, and after the umpiring crew consulted with supervisor Dave Yeast, Homolka's decision was reversed and Melillo was reinstated.
"He really didn't plow through him," Tanner said. "He kind of held up a little bit. Nobody went to the ground. You'd hate to see a player ejected in a game like this."
Jim Paronto, secretary-editor to the NCAA Baseball Rules Committee, said in a statement that Homolka initially believed the collision was caused by a flagrant act by Melillo but it was later determined that it was not.
"I was coming down the line and I could see Landon telling me to get down," Melillo said. "I was kind of looking to see where Liuzza was going to go, where the ball was going to take him, so I could try to take an angle and slide around him.
"The ball led him up the line and we collided a little bit. It was nothing intentional. He understood that."
The intent of the rule is to encourage base runners and defensive players to avoid violent collisions whenever possible.
"I'd be surprised if it wasn't reviewed," Yeast said.
It was the second CWS game in which the collision rule came into play. Georgia shortstop Justin Holmes was ejected for running into catcher Nick Hundley in the Bulldogs' 8-7 win. Holmes was out on the play.
The Gamecocks went on to score four more runs in the inning, three on throwing errors by the Tigers. South Carolina added six more runs in the eighth inning to seal the victory.
LSU (46-19) was knocked out of the CWS in two games for the second year in a row by South Carolina.
LSU, which had won two of three regular-season meetings between the teams, was dealt its worst loss since being beaten 15-4 by Mississippi State in 2002. It was the Tigers' worst loss in the CWS since Cal State Fullerton beat them 20-6 in 1994.
"We didn't defend the field well for a few innings," LSU coach Smoke Laval said. "We usually avoid the big inning, but this time we didn't and it seemed to snowball on us. We just needed a few more timely hits."
The teams combined for a CWS-record 34 singles. South Carolina's Steven Tolleson had the game's only extra-base hit, a double in the ninth.
Steve Pearce had four singles for the Gamecocks, and LSU's Will Harris had three.
Gamecocks starter Aaron Rawl (13-4) got the win after scattering 11 hits over 6 2-3 innings.
Hurricanes Downed By Cal State Fullerton, 6-3
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