During the 1998 NHL entry draft, Antropov was only expected to be drafted in the early second round, but due to a dominant season with Kazzinc Torpedo Ust-Kamenogorsk in the second-tier of the Russian Super League, he was drafted tenth overall by the Maple Leafs. Before going overseas to play hockey in North America, Antropov also played in the Russian Super Liga with Dynamo Moscow.
When Owen Nolan joined the Maple Leafs in March 2003, Antropov changed his number from 11 (Nolan's number in San Jose) to #80, the year of his birth. In 2003-04, Maple Leafs coach Pat Quinn formed a line with Joe Nieuwendyk, Alexei Ponikarovsky, and Antropov. This line was dubbed the "Sky Line" because of the players' heights.
However, once the NHL resumed play and Antropov returned to the Maple Leafs, injures began to plague the forward, and he missed significant time during the 2005-06 season. Antropov managed to produce 12 goals and 19 assists for 31 points in 57 games in the reduced season. This was largely due to the fact that once Antropov returned from injury, he added 15 points in the final ten regular-season games of the season, despite only earning 16 points in 47 games before the injury. Antropov finished third on the team in even-strength scoring, and also led the Maple Leafs in plus-minus with a +13 rating.
In 2006-2007, Antropov typically played alongside team captain Mats Sundin and Ponikarovsky on the top forward line for the Maple Leafs. At the conclusion of the season, the Maple Leafs rewarded Antropov for his continuous improvement by signing him to a two-year contract extension.
The following season, Antropov begin to show signs of a consistent offensive presence for the Maple Leafs. In a game with the New York Rangers, Antropov scored his second career hat-trick and was named the game's first star. Due to his strong play in that season, Maple Leafs fans launched a campaign to vote Antropov as a write-in candidate for the NHL All-Star Game. Despite failing to make the team, the attention was proof of his stronger overall play.
On February 9, 2008, Antropov set a new career high in goals with 19 when he scored in overtime to give the Maple Leafs a 3-2 win, tipping in an Anton Stralman slapshot. He finished the season with 26 goals.