USC starts slowly, then defeats California, 70-56

Not long after tipoff Thursday, USC’s disaster sirens blared.

Its top-notch defense: absent. Its star player: benched with foul trouble. Its deficit: ever-extending.

But the fourth-seeded Trojans’ youthful backcourt and their unassuming “monster” in the middle stepped up to shut down fifth-seeded California, 70-56, in the quarterfinals of the Pacific Life Pac-10 tournament at Staples Center.

USC kept its NCAA tournament hopes alive as it enters into a tantalizing rematch with top-seeded Arizona in a Friday semifinal at 6 p.m.

“We played with a sense of desperation, I thought,” USC Coach Kevin O’Neill said. “And nothing’s more desperate than to be [8 1/2] minutes into a game and only have three points.”

USC (19-13) trailed then by eight, still jittery from the big stage and still shocked that Cal (17-14) was playing a man-to-man defense instead of zone, USC’s kryptonite.

Shortly after that, Nikola Vucevic, averaging 17.7 points and 10.3 rebounds, picked up foul No. 2.

“When he went out,” senior forward Alex Stepheson said, “it just brought us closer together.”

Trailing 16-9, USC upped its defense to its league-best standards. Its guards locked down, then knocked down jumpers.

Then, an 18-4 run. And after halftime, a 15-4 run. And after that: ballgame, almost all without Vucevic, who scored seven points in 27 minutes.

“Nik’s carried us in a lot of games and it was our turn to carry him today,” O’Neill said.

Added Vucevic: “I was frustrated … but at the end of the day we won and that’s all that matters.”

California’s Allen Crabbe, the Pac-10 freshman of the year, scored a game-high 21 points.

USC guards Jio Fontan (12 points), Donte Smith (14) and Maurice Jones (16 off the bench) all produced, while Stepheson had 14 points and 16 rebounds, upping USC’s record to 11-1 when he has a double-double.

“Stepheson’s a monster,” Cal Coach Mike Montgomery said.

They’ll need him and Vucevic against the No. 16 Wildcats (26-6), who beat Oregon State on Thursday.

The Trojans and Wildcats split the season series, with each team winning on its home court.

But the last game, a 65-57 USC victory, carried controversy after O’Neill said before the game that Arizona star Derrick Williams was “the most protected dude I’ve seen since Michael Jordan.”

The claim that Williams is coddled by referees got into Williams’ head — he mentioned it before and after what was his worst game of the season (eight points) — and when a reporter asked Williams about it Thursday, Arizona Coach Sean Miller hijacked the question.

“No one here is going to answer a question about the officials or something that was said,” Miller said.

Miller praised USC, saying it deserves a spot in the NCAA tournament, win or lose against the Wildcats.

But O’Neill knows USC — which also beat California in the opener of its 2009 Pac-10 tourney title run —- needs to beat Arizona for that.

“If we’re fortunate enough to win,” he said, “we’ll be strongly considered to get into the NCAA tournament.”

baxter.holmes@latimes.com