Finnish striker Forss starred as Brentford battered the lowly Latics 7-0 in a Carabao Cup mismatch.
The 22-year-old filled his boots against the hapless visitors, who lie rock-bottom of the English Football League and played like it.
Yoane Wissa found the net twice, including a spectacular seventh, on a comfortable night for the Bees.
Frank said: “I’m really pleased with the performance and the attitude was bang on from the first second, and not only because we scored after three minutes.
“We kept going throughout the game, throughout the 90 minutes, which says a lot about the mentality of these players, and then we scored some fantastic goals.
“Marcus is doing all he can every day in training, and he’s a really good player.
“He scored four really good goals. I guess that needs to be a 10 out of 10.”
A tough task for the visitors got instantly tougher when they gave away a penalty with less than two minutes on the clock.
Carl Piergianni tripped Wissa in the area and Forss stepped up to tuck away the spot-kick.
Forss, leading the line with regular strike duo Ivan Toney and Bryan Mbeumo on the bench, doubled Brentford’s lead after a quarter of an hour, tucking in the rebound after Wissa’s curling shot came back off the far post.
Wissa went close with a flick which grazed the crossbar, but he got on the scoresheet with a neat finish after a fine through-ball from Mathias Jensen.
It was hard not to feel sorry for Oldham when defender Raphael Diarra turned a cut-back by Saman Ghoddos into his own net, and Forss completed his hat-trick moments later to make it five before half-time.
Forss took his personal tally to four, and Brentford’s to six, on the hour when he tucked away a cross from Mads Roerslev and Wissa scored the goal of the night with an acrobatic overhead kick to complete the rout.