Games 1 and 2 – a tale of opposites.

The 2-1 win in Game 1 in which the Black and Gold came from behind with two third-period tallies after going without a single shot on goal in the middle 20 minutes.

Game 2, the B’s bang home three in the second period to take a 3-1 lead into the third, only to have Ottawa tie it up and win it in OT to send it back to the Hub of Hockey, knotted at a game apiece.

Monday, Game 3 – all things three – in Beantown. The Marathon, the Red Sox and the Bruins – with a blue-line roster looking like a marathon treatment tent at the 26.2-mile mark. The B’s roster at TD Garden for the first playoff game in three years minus defensemen Brandon Carlo, Torey Krug, Adam McQuaid and Colin Miller. Joe Morrow in and complemented with Monday call-ups to Matt Grzelcyk and Tommy Cross from Providence. Cross dressed for Game 3.

Good news up front with the return of No. 2 center David Krejci and No. 4 Noel Acciari.

Where would Boston be without the play of Charlie McAvoy, two games into his pro career and already playing like a No. 2 defenseman? He becomes the 10th Bruin in team history in a playoff game without playing a regular season game.

McAvoy, Acciari, and Cross all registering first-ever playoff points Monday night is what might be best described as yet another opposite game

How critical is a Game 3? In playoff history, when a series is tied at one game apiece, the team that wins Game 3 goes on to win the series 67.3 percent of the time.

“It’s been a long wait for people that are used to seeing their team in the playoffs,” Bruce Cassidy said after morning skate. “Hopefully, everyone’s excited.”

Here’s what we learned as everyone was excited until 5:43 of OT when Ottawa gave itself that two-thirds chance to win the series with a 4-3 win.

Ottawa goes 3-for-3 in first-goal scoring – and more in dominant first period

A Bruins’ goal in Game 3? Score first.

Not to be – again.

Erik Karlsson airmailed a 100-foot pass to a streaking Mike Hoffman who went one-on-one to beat Rask on a third-move backhand dribbler at 7:15.

Before the crowd could digest the replay, Bobby Ryan’s short-side bid squirted to an open Derick Brassard who had more daylight than high noon, promptly making it 2-0 just 25 seconds later at 7:40.

A David Backes’ blast in alone on Anderson at 14:03 went for naught. Ditto for a Boston power play at the five-minute mark.

The B’s were fortunate to escape at 2-0 when Tom Pyatt broke in 2-on-1 with 10 ticks left but Rask held serve with Ottawa’s 10th shot on goal.

The telling stat? Boston had three shots on net after 20 minutes.

“It was definitely a terrible start on our part,” Patrice Bergeron said, “that can’t happen this time of the year. They took advantage of us, you know, not getting the first period we wanted”

Opposite second brings three-goals 48 hours apart to pull B’s even

Saturday, the Bruins put up three in the second period of Game 2.

Kevan Miller took a bad penalty at 1:54 – and Ottawa cashed in at 3:42 on a Hoffman blast from the right point right past Rask for a 3-0 lead.

Noel Acciari, playing in his first playoff game, tipped a John-Michael Liles shot past Anderson at 6:05 on shot No. 6 with Riley Nash and Liles also assisting. The Bruins returned the fast-goal favor just 42 seconds later when Backes’ breakaway took Anderson to school at 6:47 on shot No. 7 to make the game a one-goal affair; Liles and Cross also assisting.

“We were able to score a quick one right after that by [David] Backes, gave us a lot of life,” Cassidy said.

Back to back power plays gave Boston the golden opportunity to tie the game. As one expired, David Pastrnak connected with twine on a 10-ffot blast past an unflinching Anderson to tie the game at 13:31 – and set up a dramatic final 20 minutes. McAvoy and Ryan Spooner assisting.

“We picked up our game as it went along,” Cassidy said. “We had to. It was getting away from us.”

Final 20 sets stage for OT – Ryan wins it for Ottawa

Go figure. A frantic first and second period – even across the board in the final 20. Onto overtime for the second time in 48 hours with the same final score.

For the same team.

A bad penalty to Nash for roughing at 4:38 led to a Bobby Ryan tip off a Kyle Turris pass at 5:43.

“Demoralizing and disappointing,” a dejected Cassidy said about the call. “There’s probably a lot more words, but they called it. So once they call it, it’s our job to kill it.”

That didn’t happen and Ottawa takes the 2-1 series lead. They outshot Boston, 32-20.

“I think we’ve shown it all year long that we can bounce back,” Tuukka Rask said after giving up eight goals in the last two games. “They showed some great hockey today too. Just try to get a better start on Wednesday and play with the lead.”

“Another one-goal game, another tight checking game, another game where every play was magnified,” Backes said postgame.

“I expect the next one to be the same way and we get this thing tied back 2-2, you know, best of three kind of series, that’s our focus now. We’ve got to take this, digest it, and then move on because it’s in the books and all we can affect it now Wednesday’s game and come out flying in that one and take control of the game for a full 60 minutes would be a sight that would be pleasantly received I think.”

Indeed, it would.