DENVER — The Colorado Avalanche looked unstoppable early and shaky down the stretch in nearly blowing a big lead. Bottom line: The streak is alive. Nathan MacKinnon scored twice during a 58-second span in the first period, Matt Nieto added a late insurance goal and the Avalanche won their eighth straight by holding off the Sharks 5-3 on Thursday night. Carl Soderberg also scored, and Mikko Rantanen had a goal and two assists for the Avs, who’ve won eight in a row for the first time since the 2005-06 season.