Turris then got the puck to Ryan, who tipped it past Tuukka Rask as the Senators overcame blowing a 3-0 lead to re-capture home-ice advantage in the series.
It was Ottawa's sixth win in seven games against the Bruins this season, the third in as many tries at TD Garden, where the Senators have won four straight going back to last season.
The refs didn't score the overtime goal or force the Bruins to blow coverage on the deciding tally from, who else, Ryan, but it's still frustrating when the officials play such a strong factor in the outcome of a game, especially when it's a playoff game between two teams who battled pretty evenly all night long.
The Senators rallied from a 3-1 deficit with a two-goal third period to force overtime.
The Senators were able to get up off the mat after Ryan scored the victor at 5:43 of OT on the power play to deliver the knockout punch to the Bruins.
"We'll have to find a way, regroup tomorrow and get ready to play in front of our fans and we're looking forward to that", he said.
For the second straight game, the Bruins erupted for three goals in the second to bring an anxious crowd to life.
The Bruins lost Game 3 4-3 in overtime and trail the best-of-7 series 2-1. The NHL Playoff Odds for the game have the Bruins favored comfortably to pick up the win. That didn't happen on Monday night once the Bruins fell down by a couple of goals early in the game.More news: New 'Australian values' test planned for citizenship
According to oddsmakers at Bovada.lv, Boston is the clear favorite at home, as the Bruins are getting odds of -165 to win, while the Senators are being given a money line of +145 to win.
After opening the scoring with a highlight of the night goal on a hail mary pass from Erik Karlsson to spring Mike Hoffman for a breakaway, that he finished with the "Forsberg", Derick Brassard notched his second in as many games just 25 seconds later.
The Senators struck quickly with two goals in a span of 35 seconds in the first that left the probably left the Bruins wondering what it was going to take. You look at the last two games and both teams showed a lot of desperation in the third period. Backes' shot zipped through the netminder's five-hole to make it a 3-2 game at 6:47.
Fortunately for them, the Senators rebounded to take the 2-1 series lead in overtime, but not without instilling doubt about this team's ability to hold leads.
"Yeah, I was literally thinking, "Not this (crap) again, ' " MacArthur said of the Bruins" rally on Monday.
Boucher confirmed defenceman Mark Borowiecki might be available to return to play after suffering a lower body injury in Game 2.
The event capped an exciting weekend of sports in the New England city that also included an National Basketball Association postseason game between the Boston Celtics and Chicago Bulls and a weekend home stand for the Boston Red Sox.
Arguably the NHL's best defensemen, if not players, Karlsson is a generational talent.