Strome, whom Arizona drafted third overall in 2015, scored a goal and set up another on Sunday and was named Most Valuable Player of the Memorial Cup tournament by scoring seven times and racking up 11 points.
Windsor, the host of this year's four-team, round-robin tournament, was paced in the win by Jeremy Bracco's goal and two assists while DiPietro made 32 saves.
"They had more goals than us," a disappointed Strome said. "I thought we had a pretty good game."
The game was a back-and-forth classic that came down to the end. When it was over, Windsor became the 10th host team to win the Memorial Cup and the first to do so since 2012 when the Shawinigan Cataractes won.
After trading chances early, Bracco got Windsor on the board at 16:07 of the first period when he gathered up a loose puck on a Spitfires power-play chance and buried it from the slot.
That goal got the partisan crowd revved up, but Strome quieted it 48 seconds later. Picking up a pass in the slot from Darren Raddysh, Strome wired a wrist shot past DiPietro for his seventh marker of the tournament.
Strome would be at it again in the second period and his assist gave Erie a brief lead after his pass was deflected off the skate of Warren Foegele at 5:35.
Windsor struck right back less than a minute later as big defenseman Logan Stanley's wrist shot found its way through traffic and into the net. Erie then took a 3-2 lead midway through the second when a shot by TJ Fergus tipped off a Windsor stick in the slot.
The second-period scoring barrage continued and the Spitfires got things square again when Graham Knott banged home a power-play goal at 14:53. The teams headed into the final frame tied 3-3.
After a couple of near misses by the Otters to start the third period, the Spitfires took a lead at 5:07 after Bracco feathered a perfect pass to Aaron Luchuk who whistled a shot past Erie goalie Troy Timpano to make it 4-3.
That goal proved to be the winner as the Otters couldn't find the equalizer. Despite creating good scoring chances, DiPietro kept them at bay.
Strome was named MVP behind a tremendous tournament for the Otters. He led the Memorial Cup with seven goals, co-led with 11 points and established a new tournament record for points in a game with his four-goal, three-assist performance against Saint John in a round-robin game.