Junior Alex Jacobson was an afterthought when he sat out with a back injury earlier this season.

After all, 0.9 point and 1.1 rebound averages won’t stick out on a box score.

But sure enough, there the fan-favorite “”Tree”” made his presence felt this weekend, helping now-No. 21 Arizona (18-4, 7-2 Pacific 10 Conference) fight off two Los Angeles schools that had big and tall frontlines.

First it was frustrating 305-pound UCLA center Joshua Smith. Then it was Saturday against Southern California, when Jacobson played a season-high 15 minutes fending off Trojans Alex Stepheson and Nikola Vucevic.

“”It feels like I just ran a marathon. I’m exhausted,”” Jacobson said afterward. “”I had a bulging disk — three of them to be exact.””

Jacobson, who hadn’t played since a Dec. 5, 2010 game against Oklahoma, scored two points and grabbed four rebounds in 19 minutes through the two games this weekend, and head coach Sean Miller praised the defense and solid all-around play of the 7-foot center.

“”He screens, he offensively rebounds, he catches and moves the ball,”” Miller said. “”He did a nice job.””

Jacobson earned his nickname during his freshman year at basketball player factory Mater Dei High School.

“”My freshman year at Mater Dei, it was meant as an insult,”” Jacobson said. “”I got there and didn’t know what to do. Our high school coach said, ‘You’re standing there like a tree.’

“”It just kind of stuck.””

Lights out

Sophomore Derrick Williams is perhaps the most efficient basketball player in the NCAA — maybe ESPN stat guru John Hollinger can put an exact number on it — but his high quality of shot selection might be contagious.

The Wildcats are one of the best teams in the country in field goal percentages, ranked No. 18 with a 48.3 pure percentage and No. 7 in adjusted field goal percentage, which takes into account 3-pointers and thus points per shot taken.

That jump from the pure percentage to the adjusted is thanks to Arizona’s 40.7 percent 3-point accuracy, which is a tribute to Williams’ inside presence and a number of his teammates being capable shooters if they are selective enough with their shots.

“”We’re not a team that relies on that one or two (players),”” Miller said. “”We have five or six different players. Because of that, it allows us to be more consistent.””

And of course, Williams isn’t too shabby himself, shooting a whopping 70.6 percent from the 3-point line. Saturday, he hit all three attempts despite a heavy wrap on his shooting hand.

“”He doesn’t shoot that way in practice all the time,”” Miller said. “”He’s such a gamer.””

Great quotes

Arizona fans might know firsthand that USC head coach Kevin O’Neill isn’t one to censor himself.

Such was the case for O’Neill and his center, Vucevic, after USC fell to the Wildcats.

“”I felt like we played like women today,”” Vucevic said. “”We weren’t aggressive, we didn’t handle the ball well, and we were slow.””

Vucevic, a Montenegro native, publicly apologized through the Los Angeles Times Sunday night for his comments after the game.

“”I didn’t mean to offend people,”” Vucevic told the Times. “”If I did, I apologize for it.””

“”Back home, when we say that, it means we didn’t play hard,”” he added. “”It’s just a saying we have.””

Although Arizona led by as many as 20 points during the game, the nine-point loss for the Trojans might have been a different story had USC not shot 13-for-25 at the free throw line.

“”That went right along with the tone of the game,”” O’Neill said. “”It was abysmal.””

Wildcats in Top 25, tied for first in Pac-10

Though they had adopted the mantra of “”we never left”” this season, in the opinion of coaches and writers who vote in the top 25 polls, the Wildcats had indeed left.

But on Monday, Arizona was back, debuting in the Associated Press Top 25 ranking and returning to the ESPN/USA Today Coaches Poll. It’s the first time the Wildcats have appeared in both polls since Dec. 31, 2007.

The Wildcats are now ranked No. 21 in the AP and No. 22 in the coaches’ poll.

They were aided as 17 teams from last week’s ESPN/USA Today Coaches Poll recorded at least one loss this past week.

Arizona is now tied for the conference lead after No. 17 Washington lost its only game this weekend against Washington State.