Before manager John Farrell could reach the crew to argue, they had left the field for review.
Crew chief Jeff Kellogg came out shortly and ruled it a homer.
"I was just rounding first, but it looked like it bounced up in the air on the way back. It didn't look like it hit right off the wall in play," Lavarnway said, "so I had a pretty good idea it was out."
The home run was the Red Sox's sixth of the game, marking the first time since 2011 the Red Sox hit six homers at Fenway Park. By the end of the eighth inning, Boston had hit eight home runs in a game for the second time in team history.
Jason Mastrodonato is a reporter for MLB.com. Follow him on Twitter @jmastrodonato. This story was not subject to the approval of Major League Baseball or its clubs.