Entering Wednesday’s contest, the Washington Capitals hadn’t lost to the Ottawa Senators in D.C. since March 12, 2006, going 11-0-2 in their last 13 games at home against Ottawa. Make that 11-1-2 now, as the Caps frittered away a 3-1 second period lead, falling to the Sens 6-4 before a bewildered capacity crowd at Verizon Center.

Head coach Adam Oates was visibly frustrated in his post-game remarks, saying, “If guys don’t know that we let one get away, shame on them.”

The Caps got on the board first at 12:10 of the first period. Michael Latta carried the puck to the left wing dot, where he was upended by an Ottawa defender. Eric Fehr swooped in on the loose biscuit and lifted it cleanly past Craig Anderson for his second goal of the season.

Mike Green took a hooking penalty right after the goal, though, and the Senators made him pay, as Bobby Ryan tipped in a shot from the center point by Patrick Wiercioch to even it at one apiece.

The Caps got it right back. Moments after Zack Smith went off for hooking Nick Backstrom on a offensive zone faceoff, Alex Ovechkin passed to the crease. The puck caromed off Troy Brouwer and a defender and went right to Marcus Johansson, standing alone at the right post. All Johansson had to do was push the puck in for a 2-1 lead.

Washington extended the lead to 3-1 just a minute later. Brooks Laich won the puck in the left wing corner and knocked it to Jason Chimera. Chimera’s pass bounced off Joel Ward and with Laich moving to the net, he corralled the loose puck and slipped it five-hole on Anderson.

That’s when things got silly for a bit, and actually changed the momentum of the game. Senators’ forward — and noted pugilist — Chris Neil took a run at Nate Schmidt, delivering a big blow to the Caps defenseman. Neil was whistled for interference on the hit, but Tyson Strachan decided he needed to stick up for his fallen defensive partner and he fought Neil. Strachan was hit with an instigator penalty and 10 minute misconduct to go along with five for fighting, negating what should have been a Caps power play for Neil’s original infraction.

Strachan said he didn’t see the ref signal the original call against Neil and said he felt like he was “doing his job.” Both Oates and Brooks Laich defended Strachan stepping up for his teammate. But it’s undeniable that Ottawa got the better of the momentum from the exchange and that Neil, a veteran, took advantage of the situation to pump some life into his until then moribund team.

The fights carried over to the second period. Aaron Volpatti delivered a heavy body check on veteran Colin Greening, and Greening, who is struggling mightily this season with no goals and just three assists so far, retaliated with a slash to Volpatti’s thigh pads, then both players dropped the gloves.

The Senators then cut the lead to one at 6:36 of the second. With Eric Fehr in the box on a tripping call, defenseman Chris Phillips walked in on the left wing, wound up, and fired a slap shot past the glove hand of Braden Holtby to make it 3-2. It was Phillips’ first goal of the season.

Greening got that first goal a little later in the period. Immediately after springing from the box following his fighting penalty, Greening bore down the right wing and fired a laser past Holtby’s glove side to tie the proceedings at three — and leave the Verizon Center faithful with slacked jaws.

The Senators outshot the Caps in the period 19-3.

The Capitals’ penalty parade continued in the third, as Fehr went off for his second tripping call of the game. Ottawa made good on it right away, with Mika Zibanejad tipping in Jason Spezza’s shot from long distance as he skated through the crease unmolested.

Things continued to go poorly for the Caps for much of the third period, but they got a gift with 3:30 remaining, as John Carlson was hauled down by Zack Smith as Carlson was trying to keep a puck in the offensive zone. On the ensuing faceoff, Joel Ward won the draw and the puck came right back to Carlson at the point, and his wrist shot got through a maze of bodies and went over Anderson’s left shoulder to tie the game at four.

But the Caps couldn’t stand their own good fortune. Just over a minute later, Zack Smith split Mike Green and Schmidt and sent a wrist shot toward net that Holtby simply misplayed, and the Senators retook the lead at 5-4.

An empty net goal by Bobby Ryan with 12.6 second left provided the final margin of defeat.