"I'm pretty speechless right now," said an emotional Costello after his team's 44-34 win over LSU.
Costello, who transferred to the Bulldogs this offseason following a disappointing stint at Stanford, finished his postgame interview by seamlessly dropping his new conference's slogan.
"The SEC, it just means more. I can't say anything more than that," he said, according to Kyle Bonagura of ESPN.
Costello threw five touchdown passes during his memorable outing. He also had two interceptions.
Three Mississippi State players - running back Kylin Hill (158 yards, one touchdown) and wide receivers Osirus Mitchell (183 yards, two touchdowns) and JaVonta Payton (122 yards) - went over 100 yards receiving.
In characteristic fashion for an offense helmed by head coach Mike Leach - who was also making his Bulldogs debut - Mississippi State produced only nine yards rushing on 16 attempts.
But the lack of a rushing threat ultimately didn't matter as Costello threw two fourth-quarter touchdowns to seal the win, much to Leach's delight.
"It's better than average, I'll tell you that," the head coach said of his impressive first game with Mississippi State.