Updated

Erik Karlsson and Chris Kelly scored on power plays in the second period and the Ottawa Senators ignored their underdog tag and the Pittsburgh Penguins' recent playoff success, surprising the Stanley Cup champions with a 5-4 victory in Game 1 of the Eastern Conference first-round series Wednesday night.

Evgeni Malkin scored twice following penalties on Peter Regin, the first barely 3 minutes into the game, but the Penguins looked mostly flat and uninspired for long periods in beginning their bid to become the NHL's first repeat champion since Detroit in 1998.

Sidney Crosby, who piled up 15 points in his final five regular-season games, had three assists but was held without a shot until getting two in the third period and the Penguins -- seemingly unprepared for Ottawa's defensive pressure -- were held to a single shot during a stretch lasting 21 minutes, 53 seconds. Ottawa constantly matched shutdown defensemen Anton Volchenkov and Chris Phillips against the Crosby line.

The Senators, one of the biggest underdogs of the first-round qualifiers, went from being down a goal to being up 3-1 during that period as Regin, Chris Neil and Kelly scored -- quieting a standing-room crowd of 17,132 that clearly arrived expecting another long playoff run by the home team.

Goalie Brian Elliott gave up four goals on 21 shots in his playoff debut, but made several big stops on Alexei Ponikarovsky and Malkin in the second period as the Penguins pressed to tie it following Malkin's second goal, at 10:22.

Instead, the 19-year-old Karlsson restored Ottawa's two-goal lead less than 3 minutes later, collecting a rebound of a shot from the left point by Matt Cullen that rebounded off Mike Fisher in front and wristing it into a wide-open corner of the net to make it 4-2.

The Senators also got a fortuitous bounce on Kelly's goal at 1:20 of the second that put them up 3-1. Chris Campoli was attempting to wrap the puck around the boards, but it took an odd deflection directly to Kelly close to the net with no defender near him. Kelly also had two assists.

Pittsburgh made several more pushes, with Craig Adams scoring at 5:16 of the third after playing all 82 regular-season games without scoring. He scored three goals during last season's playoffs.

Again, the Senators answered as former Penguins agitator Jarkko Ruutu accepted Neil's giveback pass to beat Marc-Andre Fleury on a wrist shot at 9:40 of the third. Ruutu began the rush by controlling the puck along the boards and feeding it up ice. Fleury faced 26 shots.

Alex Goligoski cut it to one goal again by scoring with 2:14 remaining, but the Penguins couldn't tie it even as their white shirt-wearing fans stood, chanting, "Let's Go, Pens!'' for most of the final 2 minutes.

The Penguins won seven of eight playoff rounds during the previous two seasons, losing only to Detroit in the 2008 finals, but this time they almost seemed to relax after Malkin scored off Sergei Gonchar's pass on their first power play of the postseason. The goal came almost too easy and, rather than building on the early momentum, Pittsburgh allowed it to slip away and Ottawa tied it on Regin's goal at 8:45 off a long rebound.