Horvat scored his second goal of the game with 0.1 seconds left to play as the Knights defeated the Barrie Colts 3-2 in Game 7 of the OHL final on Monday.
Alex Broadhurst directed the puck toward the Barrie net and it came loose close in the crease for Horvat to slip past goalie Mathias Niederberger. The goal — at 19:59 — required a video review to confirm both the time remaining and whether the puck actually crossed the line.
"You dream as a kid about scoring a goal like that in a Game 7," said Horvat. "I knew I had to get to the net and look for a rebound."
Horvat, who also scored 7:13 of the first period to open the scoring, finished the series with seven goals and four assists, and was named the winner of the 99 Trophy as playoff MVP. Horvat had 16 goals and seven assists in 21 playoff contests.
"It's unbelievable to win the 99 Trophy," Horvat said. "I'm humbled to have my name going on that trophy with all the other great names. I certainly couldn't have done it without all the other guys in our room."
London becomes the first back-to-back OHL champions since the Windsor Spitfires in 2009 and 2010. Last year, the Knights lost in the Memorial Cup final in overtime, 2-1 to Shawinigan.
Despite the tension during the video review, London captain Scott Harrington said he gradually became confident of the outcome.
"The longer the time for the review went on, the better the chance I knew it would be a good goal," said Harrington, a Pittsburgh Penguins prospect.
Andreas Athanasiou had scored midway through the first for Barrie to even it 1-1. The former Knight had a yawning cage to fire the puck into after a terrific pass from Zach Hall. It would be Barrie's lone power-play opportunity.
Olli Maatta's power-play goal in the second period restored the London lead. The blue-liner had left his point position and received a pass from Broadhurst before beating Niederberger.
London maintained its 2-1 advantage until Mitchell Theoret's 14th of the playoffs at 17:09 of the third created the electric finish in front of 9,046 at the Budweiser Gardens.
The tension included a Barrie shot off the crossbar with just over two minutes remaining.
The Knights now join host Saskatoon Blades, WHL champion Portland Winterhawks and QMJHL winners Halifax Mooseheads at the Memorial Cup, which begins Friday with the Blades entertaining London in the tourney opener. Saskatoon has been idle since March 27, losing in the first round of the WHL playoffs.
Theoret had one goal and one assist for Barrie as the Colts had led the best-of-seven 3-1 before losing 6-4, and 5-4 in overtime to force the decisive seventh game. The Colts played without OHL playoff scoring champion Mark Scheifele (15 goals, 41 points), who was injured in Game 6 in Barrie.
Jake Patterson stopped 30 of 32 for London for his third post-season win in three consecutive starts. Anthony Stolarz had won London's first 13 in the playoffs.
Mathias Niederberger faced 48 shots, including Barrie trailing that stat 39-17 after two periods.
The Colts' only OHL title was in 2000, when they outlasted Plymouth in seven games, clinching that year on the road.