ST. CATHARINES, Ont. - The Niagara IceDogs let one slip away.

Owen MacDonald scored at 2:58 of overtime as the London Knights came from behind for a 6-5 win over the host IceDogs on Monday in Game 3 of the Ontario Hockey League final.

Niagara held leads of 4-1 and 5-2 before the Knights surged back for the victory. London leads the best-of-seven series 3-0 and can claim its third J. Ross Roberston Cup in the past five seasons.

Game 4 goes Wednesday in St. Catharines, Ont., at the Meridian Centre.

Matthew Tkachuk, Cliff Pu, Olli Juolevi, Christian Dvorak and Victor Mete also scored for the Knights. Jacob Graves chipped in with four assists while Mitch Marner added to his playoff scoring lead with a pair of helpers.

The Toronto Maple Leafs prospect has 16 goals and 43 points in 17 post-season games to lead all OHL skaters. He's only been held off the scoresheet once — in Game 2 of London's first-round series against Owen Sound.

Josh Ho-Sang scored once and set up two more for the IceDogs, who got a goal and an assist apiece from Vince Dunn, Pavel Jenys, Stephen Harper and Ryan Mantha.

Niagara led in shots 17-4 after the first period but were outshot 35-13 through the final 40 minutes of regulation and overtime.

London's Tyler Parsons had a shaky start with four goals against in the first period, but finished the game with 25 saves to earn the victory. Parsons had allowed just five goals in his last five starts heading into Game 3. Niagara's Alex Nedeljkovic stopped 33-of-39 shots in a losing cause.

Forward Max Jones returned to the lineup for the Knights after serving a 12-game suspension handed out in Game 4 against Owen Sound for a blindside hit on Justin Brack. The last time he dressed was March 30.

London won the league title in 2012 and 2013. In 2012 London beat Niagara 4-1 in the finals — the only other season the IceDogs franchise made the championship.