It's a good thing Matt Mullen is not resistent to change.

In fact, right about now, he would recommend doing things differently to just about every person with whom he comes in contact. Speaking of contact . . .

Mullen yesterday went a perfect 4-for-4 with two doubles, along with four RBI, as Monsignor Bonner High bested Ss. Neumann-Goretti, the defending Catholic League champion, 9-5, in a rousing semifinal at Widener University.

The Friars' opponent in Tuesday's all-Red final, also at Widener at 3:30, will be Archbishop Ryan, a 9-8 winner over Archbishop Wood.

The switch-it-up thing for Mullen, a 6-foot, 165-pound senior rightfielder, goes back to the beginning of the season, and we'll let him explain.

"The last 3 years," he said, "I always took a lot of pitches because I was trying to get on any way I could. I've come to learn that pitchers so often throw first-pitch fastballs, so now I go up there looking to swing right away."

Part Two came recently.

"I hit second in the order all season, but then they decided to move me to third," Mullen said. "They told me I could be more relaxed in that spot and could go in there just worrying about swinging [aggressively]. Before I always had to think about moving the leadoff guy along.

"Really, they were going to have me hit cleanup. But that would have meant starting the game with three straight lefties with Rick Reigner, Sam Christie and Alex Liberatore, so they decided to put me third, with Alex fourth."

If you blinked in the home first yesterday, you missed a lot.

Each of the first four hitters swung at the first pitch! Reigner doubled to left-center, Christie did likewise, Mullen's check swing yielded an infield hit and Liberatore hit into a doubleplay.

"I was talking to Rick before the game, how he should go up there ready to swing," Mullen said. "There'd be a chance to set the tone. Sam followed up and then everyone else did, too. Neumann was the talk of the league all season [with five returning starters, two quality transfers]. We were really fired up to play them."

Bonner lashed 13 hits against senior righthander Albert Baur and sophomore lefty Joey Gorman, with seven going for extra bases. Christie joined Mullen in the two-doubles club while Reigner had his aforementioned one and Josh VanHorn launched a double and triple.

Nevertheless, the score was 5-5 heading into the home sixth.

VanHorn tripled, Paul Shepherd grounded out (with VanHorn holding), Matt Ruggieri lofted a sac fly for the game-winning RBI, pinch-hitter Ron Scull singled, Reigner absorbed a pitch, Christie walked to load the bases and, boom!, Mullen unloaded 'em with a double high off the massive fence in left-center.

"Since we already had the lead," he said, "I was just looking to get a hit to keep the momentum going. It wasn't like we needed a big hit. It was a fastball left out over the plate. I knew I hit it good. Maybe not that good.

"We were focused," he said. "We really wanted to do this."

The win went to junior righthander Matt Dolan, provider of two no-hit shutout relief frames. N-G's leader was Mike Riverso (three total RBI), whose 400-plus-foot, two-run homer to dead center made it 5-5 in the fifth.

Meanwhile, Mullen is part of quite the athletic family. His cousin, Kyle Mullen, now at Saint Joseph's University, last year was the Daily News' Pitcher of the Year for his work at St. Joe's Prep. His uncles, Kevin and Terry, were football/baseball All-City honorees at Archbishop Carroll. Matt's dad, Tony, the oldest of eight (five boys), is a Bonner assistant.

Matt, who lives in Drexel Hill, is headed for Saint Joe's and figures to major in business. That's what he gave yesterday to all baseballs that approached his bat.