Some things, you just know are going to be difficult for a team like the Mavericks, and beating the Shamrocks on St. Paddy’s Day certainly was. Yes, even these woeful Boston Celtics, who bear no resemblance whatsoever to their highly successful ancestors of this proud franchise. Like the queen of hearts on Valentine’s or the black cat on Halloween, the Celtics were hard to handle Monday night before the Mavericks finally persevered with a couple of clutch late plays and survived for a 94-89 victory at American Airlines Center. “I feel especially fortunate that we were able to beat these guys on St. Patrick’s Day,” Mavericks coach Rick Carlisle said. “Playing the Celtics on St. Patrick’s Day, that’s not exactly a good situation, even if you’re at home.” Usually these days, all that has to happen is for the Celtics to show up and be the Celtics, and the opponent ends up smiling. But the Mavericks ran into problems late and nearly blew what should have been a routine victory. They didn’t exactly start their eight-game homestand with a vintage effort, but they did enough. Devin Harris and Monta Ellis made big offensive plays, and Vince Carter blocked a shot in the final 8 seconds to preserve the win. “We made enough plays to steal this one, but it definitely wasn’t pretty,” Dirk Nowitzki said. “We shot low-40s. That’s usually not a recipe for us to win.” A strong smattering of green around the arena meant fans were willing to celebrate St. Patrick’s Day, even though the Mavericks treated the third quarter like a holiday when their 15-point lead crumbled to three. And they took off for a large chunk of the fourth quarter, too. Overall, it looked like a game between two tired teams who had played Sunday night. Even so, the Mavericks won for the 41st time, assuring a nonlosing season for the 14th year in a row. They even survived a miserable rebounding night, thanks in part to Harris, who continues to roll as arguably the Mavericks’ most effective guard. When the Celtics were within 70-66 early in the fourth quarter, Harris tossed a lob to Brandan Wright for a dunk, then stole the ball on the other end and, from the seat of his pants, hit Nowitzki with a pass for a breakaway dunk. Then Harris cut to the basket, was fouled, and made two free throws for a 76-66 advantage with 7:33 to play. The feed to Nowitzki was a hot topic postgame. “I had to chase that one hard,” the slow-footed Nowitzki said of the lead pass from Harris.