Impossible comebacks don't happen very often. In fact, they had only happened two times in hockey before the spring of 2010.
After they both pulled off first round upsets, the Boston Bruins and Philadelphia Flyers met in the second round in a rematch of the Winter Classic, which Boston won 2-1 in overtime. Boston also looked like a sure thing to win the series, as they took the first three games of the series and had a stranglehold on the Flyers. Game 4 went to overtime, and Philly knew that if they gave up the next goal, they would be swept and their season would be over. That would not happen. The Flyers scored the overtime winner to keep them in the series.
Still, Boston looked like a lock to win, as they headed home for Game 5 with a commanding 3-1 lead in the series. However, they were embarrassed in front of their home fans and suffered a 4-0 loss to send the series back to Philadelphia. In Philadelphia for Game 6, the Broad Street Bullies continued the magic with a 2-1 win to force Game 7 in Boston.
Ironically, Boston took a 3-0 lead on the Flyers in Game 7, just like the series. It seemed as if the Bruins would nearly slip away and avoid the shocking upset; however, the Flyers fought back. They scored four consecutive goals to win their fourth consecutive game in the series, and pulled off potentially the greatest comeback of all time.