By David Ljunggren

OTTAWA (Reuters) - Matt Cooke scored twice as the Pittsburgh Penguins fought back from a 3-0 deficit to beat the Ottawa Senators 4-3 in overtime on Saturday and win their first round NHL playoff series.

Pascal Dupuis scored the winning goal at 9:56 in the first period of overtime to seal victory for the Stanley Cup champions, who had trailed 3-0 midway through the second period.

In other action, the Chicago Blackhawks beat the visiting Nashville Predators 5-4 in overtime to take a 3-2 lead in their Western Conference series.

Chicago's Patrick Kane scored a shorthanded goal with 13.6 seconds to go to tie the game before Marion Hossa scored in overtime.

Ottawa initially looked the sharper of the two sides, who had played into the third period of overtime in Thursday's Game Five in Pittsburgh before the Senators won 4-3.

Matt Cullen scored from a breakaway 5:19 into the first period, Chris Neil netted from close range 1:51 into the second period and when captain Daniel Alfredsson scored with a wrist shot almost eight minutes later, the game looked over.

Cooke, however, sparked the comeback just over a minute later when he scored from close range.

"If you're down 3-0 you need a little wake up call and we have some leaders in the locker room who stepped up in the second intermission. It was big for us," said Dupuis.

Pittsburgh came out stronger in the third period, with Bill Guerin scoring a power play goal at 7:03 before Cooke tied the game at 3-3 from close range five minutes later.

"There were points where it was difficult to handle in terms of the score ... but our guys were rock solid."

"We have a lot of character," Clouston told reporters. "We don't quit. We battled right to the end."

(Editing by Greg Stutchbury)