Mascherano, 40, is a former teammate of Miami star Lionel Messi. The two were teammates at FC Barcelona from 2010-18.
Miami had won the regular season campaign with a record points total but after losing twice in the best-of-three series, the MLS Cup favourites and their eight-times Ballon d'Or winner are out.
Portuguese winger Xande Silva blasted home a sensational winner for Atlanta in the fourth minute of stoppage time in front of 68,455 home fans at the Mercedes-Benz Stadium to level the best-of-three postseason series 1-1 and set up a winner-take-all game three in Miami next Saturday.
Miami started with all their big-name stars, including Lionel Messi, on the bench but the Argentine was introduced in the 61st minute to the delight of many in the Toronto crowd.
Messi had been subdued until the 45th minute when he put Inter ahead -- chesting down a long ball into the box and getting a lucky bounce off Crew defender Malte Amundsen before poking home.
Messi tied Saturday's match in the 67th minute when he lasered a shot from beyond the box that evaded diving Charlotte goalkeeper Kristijan Kahlina to make it 1-1.
Inter Miami's charge towards Major League Soccer's single-season points record suffered a setback on Saturday after a last-gasp injury-time equalizer from James Sands snatched a 1-1 draw for New York City FC against the Eastern Conference leaders.
The Argentinian superstar Messi came close to a game-clinching goal in the 83rd, but his angled effort was blocked by Atlanta goalkeeper Brad Guzan and Suarez's attempt to tap in the rebound was also denied.
The eight-times Ballon d'Or winner hadn't played since injuring his right ankle during the Copa America final on July 14, when he helped Argentina to victory over Colombia.
"Very happy to get the first title in this club's history. Everyone's hard work and commitment made it possible. Hopefully this is just the beginning," Messi posted on Instagram
Messi overtook former Barcelona teammate Dani Alves who had won 43 trophies in his career.
Messi had put Miami ahead in the 24th minute with a wonder strike into the top corner but Fafa Picault levelled for Nashville in the second half
Lionel Messi could clinch his first trophy with Inter Miami, just four weeks after making his debut for the club, when his team face Nashville in the final of the Leagues Cup in Tennessee on Saturday.
Lionel Messi said Thursday he has refound happiness since joining Inter Miami, describing his move to Major League Soccer as the "opposite" of his transfer from Barcelona to Paris Saint-Germain.
Argentina superstar Messi took his tally to nine goals in six appearances for Miami in an entertaining semi-final at Philadelphia's Subaru Park.
Messi scored in his third consecutive match for Inter in a 3-1 victory over Orlando City last week, helping them move into the last 16 of the tournament.
Major League Soccer team FC Dallas’ owner Dan Hunt was in awe of Inter Miami’s Lionel Messi after his side lost to Messi’s heroics as Miami advanced to the Leagues Cup quarterfinals on Sunday.
A trademark curling free-kick in the 85th minute, Messi's seventh goal in his fourth game for Miami, took the game to the shootout after Miami had trailed 4-2 with 10 minutes to go.
Orlando City head coach Oscar Pareja says his team's defeat to Lionel Messi's Inter Miami on Wednesday was a "circus" and said that the Argentine should have been sent off.
