DANVERS – The hallmark of any Andover team is defense, tailored for its opponent and always aggressive.Forcing the ball away from St. John’s Prep’s wing players last night forced the top-ranked Eagles into a little more one-on-one play than they’re used to. This in turn limited possessions and, when it counted more, gave the visiting Warriors a lot of momentum.A war of a fourth quarter ended with a huge driving layup from sophomore guard David Giribaldi at the buzzer to send the game to overtime, and a 7-2 run to finish overtime earned eighth seed Andover the upset of the Division 1 North tourney, 62-59.Now 16-6, the Warriors will move on to play Central Catholic in the semifinals. St. John’s Prep sees its promising season end at 19-3.”Andover is a physical team, and in the second half they did a much better job of defensing our guards out of the lane,” said Eagles head coach Sean Costello. “Then they did a good job getting their guys is spots to score.”It didn’t seem like that course would come to pass early on, as senior forward Josh Syska (16 points and 14 rebounds before fouling out in overtime) and point guard Tyler Dooley (16 points with an injured ankle) got the Prep out to a quick six-point lead six minutes into the game.Junior Max Burt was huge in the second half, hitting St. John’s only two three-pointers and finishing with 10 points, all in the final 20 minutes.”Max always helps us,” said Costello. “He’s an energy guy, he got some big steals for us (one in OT for the Eagles’ last lead of the night), and he always does good things for us.”But Andover kept sniping back, never letting the lead extend past two possessions. And when Sam Dowden (game-high 19 points with two 3-pointers) asserted himself in the paint in the second half, blocking a pair of fourth-quarter shots, combined with a clutch three from Chris Dunn (eight points), the Warriors drew even with 1:21 left in regulation.Syska seemed to send the Eagles to victory when he hit a short baseline jumper with seven seconds left, but Giribaldi took a long pass, drove to the hoop and scored. A conference between the three referees ruled the layup beat the buzzer.In OT, Andover forced three turnovers, the last with 21 seconds left on a traveling call with the Prep trailing by a pair. A traditional three-point play from Dowden and a pair of free throws from Dunn gave Andover a three-point advantage, and when an air-balled 3-pointer flew into Dowden’s hands at the buzzer, the upset was complete.