NORTH BILLERICA – Lightning didn’t strike twice for the Marblehead boys hockey team on Thursday in the Division 3 North semifinals at Chelmsford Forum.The Headers avenged last season’s shootout loss to Shawsheen as Ryan Dempsey scored twice and Tony Cuzner stopped all 17 shots he faced in a 3-0 win over the Rams.Click here for a photo gallery.”We told the kids that we were proud of how hard they worked and their effort,” Marblehead coach Bob Jackson said. “We had a dominant first period and played well from there.”Marblehead never let the Rams get any flow going offensively, outshooting them 30-17.”We knew they were going to come at us,” Jackson said. “But the kids stayed with the plan and executed well.”The Headers (19-2-3) came out of the box slow but as the first period progressed, the champions of the Northeastern Conference’s South division assumed control of the contest.Dempsey sent Marblehead on its way midway through the first when he collected a Chris McLeod rebound off the backboards and roofed it past Ryan Maskell.”Ryan has been playing so well lately,” Jackson said. “He’s kind of put the team on his back the last few games.”Marblehead continued to pepper the Shawsheen goal but looked like it would have just the lone goal to show for it until a quintet of talented defensemen hooked up in the final seconds.Jackson stuck his five top defenders on the ice for the last shift of the period and caught gold when Anders Gundersen fired home Jay King’s pass from the right point with 8.2 seconds left for a 2-0 lead after one.”That was kind of a brainstorm of coach (Mark) Tarmey and it lets us take advantage of Jake and Anders’ talents up front,” Jackson said. “And it was a big goal at a perfect time.”In the second, the Rams came out with a jump in their step and pressured Marblehead. But Tony Cuzner’s point-blank save on Mike Walls shifted the momentum back Marblehead’s way.Dempsey then took advantage of a turnover by a Ram defenseman for a tap-in goal and a 3-0 lead.From there, the stingy Marblehead defense and Cuzner slammed the door on the Rams over the final 25 minutes.In the third, Cuzner stopped all seven shots he faced to preserve the shutout and the final date (against Concord-Carlisle at the Chelmsford Forum Saturday at 5:40).