Bruins losing their way in third

When the Boston Bruins won the Stanley Cup in 2011, their championship was built on defense.

It started with goaltender Tim Thomas, who won the Conn Smythe Trophy, and worked its way through the Bruins' defensive corps. The team produced enough offensively to claim its first Cup in 39 years.

The Bruins' defense was their driving force again last season, during which they were 32-0-0 when leading after two periods (Thomas was in goal for 24 of those games). They also were 38-0-0 in games they led by two or more goals at any time.

During this lockout-shortened, 48-game season, the Bruins are not showing the same late-game killer instinct they have in the past.

According to Elias Sports Bureau, the Bruins had the NHL's best third-period goal differential (plus-12) in their first 18 games this season. In the past 10 games, however, the Bruins' third-period goal differential is minus-6, which is tied for the third worst in the NHL over that span, along with the Philadelphia Flyers and Edmonton Oilers:

The alarming issue is that the Bruins' goal differential of plus-12 in the first two periods in the past 10 games ranks as the best in the league.

So what's happening in the closing 20 minutes?

In the past 10 games, the Bruins rank third in the NHL with 98 shots on goal during the third period. But there is a difference between shots on goal and quality scoring chances.

In the first 18 games of the season, Boston scored 20 third-period goals and allowed only eight, posting a 14-2-2 record. In the past 10 games, the Bruins have scored only four goals in the third period and have allowed nine for a 5-4-1 record.

But forget their lack of third-period scoring for a second. What their woes really come down to is on defense.

In the Bruins' first 18 games, they had the best third-period save percentage (.958) in the league. But in the past 10 games, that percentage has dropped to .880, which ranks 22nd in the NHL. Boston's save percentage (.943) in the first two periods in the past 10 games ranks fifth in the league.

Here's another interesting stat: The Bruins are allowing fewer third-period shots (7.6) in their past 10 games than they did in their first 18 games (9.3). So opponents are scoring more goals on fewer shots.

Some of that could be a matter of the opposition getting the bounces of late, but as we said, all shots are not created equal, so it's safe to say the Bruins are yielding higher quality opportunities in the third period during this stretch.

The numbers indicate Boston's blueliners uncharacteristically have struggled in the third period.

In the team's first 18 games, Bruins defensemen had a third-period plus/minus rating of plus-15, which was tied for second in the league. In the past 10 games, it's a minus-11, which is second worst in the NHL.

From a goaltending standpoint, the performances of Tuukka Rask (14-4-3, 1.92 goals-against average and .928 save percentage) and Anton Khudobin (5-2-0/2.30/.920) have slipped a little.

According to ESPN Stats and Information, Rask has allowed six goals in the third period or overtime in March, compared to the five he allowed during the third period in the previous two months combined.

Opposing teams seem to have figured out Rask's weaknesses. Of the 41 goals he's allowed this season, 39.02 percent have been scored to his high glove side. In fact, of the 15 goals he's allowed this month, seven of them were to his high glove side (47 percent).

The other goals he allowed were low glove (2), low stick (1), five hole (1) and open net (4). "Open net" is defined as a play in which the goalie is on the ice but out of position and without a reasonable chance of making a save.

In seven games this season, Khudobin has allowed a total of 16 goals, seven in the third period. As far as location, opponents have scored on Khudobin to the high glove side (3), low glove (2), high stick (1), low stick (4), five hole (2) and open net (4).

The Bruins have a 9-4-1 record with 19 points when leading after two periods this season. Their points percentage (points/potential points) of .679 in that situation is the worst in the NHL.

Here are the games in which the Bruins have blown late leads this season:

FEB. 15 AT BUFFALO: The Bruins had a 2-1 lead at the start of the third period, but the Sabres scored three times en route to a 4-2 win. Khudobin was in net.

MARCH 3 VS. MONTREAL: The Bruins had a 3-2 lead, but the Canadiens scored twice in the third period for a 4-3 win. Rask was in net.

MARCH 5 AT WASHINGTON: The Bruins had a 3-0 lead after the first period, and a 3-2 lead after the second, but the Capitals tied the game at 3-3 and won 4-3 in overtime. Rask was in net.

MARCH 12 AT PITTSBURGH: The Bruins had a 2-0 lead after two periods, but the Penguins scored three unanswered goals in the third en route to a 3-2 win. Khudobin was in net.

MARCH 19 AT WINNIPEG: The Bruins had a 1-0 lead after two periods, but the Jets scored three goals (one empty-netter) in the third for a 3-1 win. Rask was in net.

The Bruins continue their four-game road trip (0-2-0) Thursday night in Ottawa. The Senators are 4-2-4 in their past 10 games and are in the midst of a three-game winning streak, while the Bruins have a 5-4-1 record in that span and are only two points ahead of Ottawa in the Northeast Division.

This is the third of five games between the teams this season. The Bruins won 2-1 in overtime on Feb. 28 at Boston. On March 11 at Ottawa, Boston won 3-2 in a shootout.