LOS ANGELES — Taj Gibson scored 17 points, including six straight in a decisive second-half run, and No. 18 Southern California defeated UC Irvine 78-55 today to win its first season opener in four years.

DeMar DeRozan added 14 points in his college debut as the Trojans' highly touted replacement for top scorer O.J. Mayo, who was a first-round NBA draft pick after one season.

Dwight Lewis had 18 points and Daniel Hackett 10 for USC, which lost openers to Cal State Northridge and South Carolina, both in overtime, and Mercer in coach Tim Floyd's first three seasons.

Darren Moore scored 16 points for the Anteaters. They kept it close throughout the first half, when they led by two points and shot 41 percent from the floor. Brett Lauer added 12 points and Zac Atkinson 10.

But the Trojans asserted themselves offensively to open the second half, while also stepping up their defense.

Leading by six at halftime, USC opened with a 23-7 run to take a 58-36 lead that was never threatened. Gibson scored eight, including two dunks and a basket off his own rebound, while Lewis had five and DeRozan four.

In the final minutes, freshman Percy Miller, better known as hip-hop star Lil' Romeo, came off the bench and grabbed one rebound.

Just like Mayo, DeRozan arrives as a newcomer with the ability to immediately make an impact on the program. The McDonald's All-American forward averaged 29.2 points as a senior at nearby Compton High. He cracked the starting lineup today, going 6 of 11 from the floor, making both his free throws and grabbing three rebounds.

Along with Mayo, the Trojans lost their No. 2 scorer, Davon Jefferson, who wasn't selected in the NBA draft. The team is coming off a 21-12 season in which it lost in the first round of the NCAA tournament.

The Anteaters were 18-16 last season, losing three of their top scorers to graduation. They fell to 1-5 against the Trojans and haven't beaten a Pac-10 school since 2005.