Cirelli tied the game in the second period and then scored 1:28 into overtime on Sunday night to give Oshawa the Mastercard Memorial Cup.
"Words can't describe what I'm feeing now," Cirelli said as the Generals celebrated their 2-1 victory over the Western Hockey League champion Kelowna Rockets. "Coming from midget hockey last year and making this team, then doing this..... we worked so hard all season and to win it is unbelievable."
The Generals won the Cup for the first time since 1990 and became the first Ontario Hockey League team to win since the 2010 Windsor Spitfires.
Tomas Soustal scored in the first period for Kelowna, which had the edge in possession and play for most of the game but got only one past solid goaltender Ken Appleby. The Rockets outshot the Generals 38-26.
In overtime, a favourable bounce sent Oshawa on an attack. Goalie Jackson Whistle stopped the first shot from Chris Carlisle but Cirelli was on the doorstep to bang in the rebound.
"I was shocked when it when in. It was an unbelievable feeling," said Cirelli.
Added Generals veteran defenceman Dakota Mermis: "You see Carlisle, an overager, get the puck to the net and Cirelli, a guy who was undrafted in the OHL, and he nails it right in and then it's all just emotions. It's so crazy."
Oshawa also beat the Rockets 2-1 in the round-robin portion of the tournament, but Kelowna played a much better game this time, rarely allowing the Generals to get their cycle game going.
"Both teams battled hard and it could have gone either way," said dejected Rockets captain Madison Bowey. "We played hard and you know what? Two great teams meet up and one team has to lose and tonight we were on the wrong side of things."
An announced crowd of 10,391 turned out for the final hockey game at the Pepsi Colisee, which is to be demolished and replaced by the 18,000-seat Videotron Centre next door.
Perhaps rusty from five days off since finishing first in the round robin, the Generals were unable get sustained pressure in the Kelowna zone.
Cole Linaker won a draw from Michael McCarron and Bowey fired a puck off the end boards that Soustal, posted at the back door, put into an open side at 15:08.
The Generals found their legs during successive power plays in the second period and tied the game at 13:50 when Cirelli broke down the left side and picked the top corner behind Whistle.
Oshawa nearly had the winner at 17:30 of the third, but video review showed Hunter Smith batted it in with a high stick.
The Generals had a veteran team that will lose most of its top players next season. Youngsters like Cirelli will be the team's future. The Woodbridge, Ont. native had 13 goals in 68 regular season games and added two in the OHL playoffs.
His two at the Memorial Cup were ones he won't forget.
"I just kept working hard and thinking 'my time will come,'" said Cirelli. "I'm just thankful I got those two goals."
Kelowna star Leon Draisaitl, who led the tournament with seven points but was held off the scoresheet in both games against Oshawa, was named tournament MVP.
Appleby was named top goaltender and Alexis Loiseau of the Rimouski Oceanic was named most sportsmanlike player.
Total attendance for nine games was 79,930, or 8,881 per game. Next year's Memorial Cup will be in Red Deer, Alta.