The Red Wings led 2-1 with 2:32 remaining in the third period, but the Bruins added an extra attacker after Detroit iced the puck. Pastrnak tied it by one-timing Marchand's pass through a crowd in the slot.
"I saw [Pastrnak], but it is tough to get a pass through that many sticks," Marchand said. "Maybe it works one time out of 10 or one out of 20, but that one got through."
Pastrnak almost missed the opportunity.
"The last time I saw [Marchand], he was rushing down the wall, so I thought he was going to shoot," Pastrnak said. "I only saw the puck at the last second, but I was able to shoot it."
Noel Acciari scored for Boston (15-9-4), which has won three in a row and is 9-2-0 in its past 11 games. Tuukka Rask made 31 saves and has won five straight starts.