The 36-year-old Nesta showed he is moving closer to making his Major League Soccer debut as he took part in both 25-minute halves of the match between mostly Impact reserve players and the club's academy at their training ground at the Claude Robillard Centre.
Nesta played the first half with former Inter Milan defender Nelson Rivas, who is close to a return from an abdominal strain. He played the second with the 20-year-old Ouimette, who this season became the first academy player to sign an MLS contract with Montreal.
''It was awesome,'' said Ouimette, of Terrebonne, Que. ''He's a great player.
''He gives you tricks on how to move, how to keep the ball in tight situations and everything. He talks to me a lot. He tells me to talk a lot too. He tells me to move the ball and not just throw it away. If I make a bad decision, he tells me what to do.''
Nesta signed two weeks ago to join his old friend and former teammate Marco Di Vaio, the Impact's first designated player.
The four-time UEFA all-star and four-time Italian defender of the year is getting close to being match-fit, although neither he nor Rivas is expected to be in the lineup when Montreal plays at Houston on Saturday night.
Coach Jesse Marsch said both should be available for a friendly match next week against seven-time French league champion Lyon.
Nesta has not given media interviews since the day he signed, but he was very vocal on the field. He also had advice for 21-year-old right back Zarek Valentin.
''Alessandro's going to help our whole team with his ability to see and identify things, to read plays,'' Marsch said. ''He talks a lot with guys.
''When you have a guy who's played at the levels he's played at and has his experience, he's a resource for the players and the coaching staff.''
Marsch said Rivas was ''really close'' to a return.
''They say with the type of abdominal strain he had, he will probably feel it for a while, but it's more about now trying to calculate how strong the muscle is,'' he said.
He listed Nesta, Rivas, Italian defender Matteo Ferrari (thigh) and American forward Andrew Wenger (hamstring) as ''day-to-day'' cases.
Their return and Nesta's debut could be a huge boost to the 7-12-3 Impact in their push for a playoff position.
The team has conceded a league-high 39 goals.
In recent weeks have been using arguably the fourth and fifth centre backs on their depth chart in Shavar Thomas and Hassoun Camara. With everyone back, Marsch will have options on defence, perhaps even using a three-man back line of Nesta, Ferrari and Rivas.
''The team has done fairly well, for the most part, but getting these guys for the last stretch of games is huge,'' Valentin said.
''Their leadership and their veteran mentality is going to be big for our team. And it's getting to the point where they're all big games.''
The starters from Wednesday night's 2-1 win over New England did not take part in the scrimmage.