HINGHAM — Down go the reigning champs, and up rises the Hingham boys hockey team’s confidence in chasing its own title aspirations.

Behind a stellar job on defense and in net Saturday afternoon, as well as three unanswered goals after facing a deficit, the No. 4 Harbormen (1-0) defeated No. 1 St. John’s Prep, 3-1, in their season opener.

Sophomore John Walsh scored his first goal to break a 1-1 tie with 9:56 left to play in a physical game with plenty of back-and-forth opportunities throughout. It paired with junior Mike Karo’s (26 saves) standout performance in net, and an empty-net goal with 15.4 seconds left to seal the deal over the consensus top team out of the preseason.

Karo, who started in net for Hingham in a Div. 1 state quarterfinal loss to St. John’s Prep last year, admitted there was at least a small feeling of revenge with the win. But starting off the year this way goes well beyond that.

“Of course we were thinking about it, we wanted to get them back,” Karo said. “(But) we looked at it as an energy boost, that we could really win. … It’s just a great game. I love this game, I look forward to it over the summer. (When) we win these types of games, it just boosts our confidence so much. Now we know we can just beat any team (and) we also know that we can do better, too.”

There was a bit of uncertainty on the defensive end to start the year – at least compared to what returns up front – after Hingham lost two of its top defensemen from last season.

Harbormen head coach Tony Messina believes there’s still a lot to clean up, but his blue liners set a good tone to build on by limiting the Eagles to just the one goal – despite SJP controlling zone time in the first and producing 12 shots on Karo in the third.

“I thought our D did a better job retrieving pucks and getting them up to the forwards,” Messina said. “Not where we want to be yet, but we’re getting there.”

St. John’s Prep senior goalie AJ Farese (27 saves) played well opposite Karo, combining with the junior for a scoreless opening frame. The Eagles then didn’t take long to get on the board in the second, as Kevin Correa scored for a 1-0 lead just over two minutes in.

Only 1:40 later, though, Cam McKenna answered on a feed from Colin Lasch to tie it at 1-1.

“I liked the fact that we were down 1-0 and came back,” Messina said. “We fought. … Just good fight from all four lines.”

St. John’s Prep’s Braeden Hurley, left, has his shot kicked aside by Hingham goalie Mike Karo during the first period of Hingham’s 3-1 victory. (Photo by Paul Connors/Media News Group/Boston Herald)

The teams continued to battle to limit chances, with Karo and Farese cleaning up whatever got through. Karo’s save on a breakaway early in the third especially stood out, keeping the score neutral. Shortly after, Walsh flashed a nifty move on a rush from right to left, sweeping in front of Farese for a 2-1 lead set up by fellow fourth-liner Walter Dzavik.

“That line’s been good all year in the scrimmages,” Messina said. “They’re all capable.”

The Eagles brought plenty of heat in response, peppering Karo to no avail despite playing man-down twice on two penalties in the final four minutes.

Hingham also won this matchup last year on the road. But this time feels different.

“To win that game up there (last year) was a little surprising,” Messina said. “(This) game felt a little bit different, a little more like a back-and-forth type game as opposed to stealing (a win). The confidence carried us pretty good last year, and this year I’m hoping the same. But it should be better, we’re starting from a better spot.”

Hingham’s Cam McKenna, rear, leaps in celebration as teammates Conal Mulkerrin, front, and Luca Guidi, center, skate over to congratulate him during a 3-1 win over St. John’s Prep. (Photo by Paul Connors/Media News Group/Boston Herald)