Marshall was preparing to give a post-game interview for Fox Sports following his team's surprise 10-8 win over the Storm at AAMI Park when he noticed the Melbourne players were getting ready to give Slater a guard of honour as he walked off the ground.
Yelling out to his teammates over the other side of the field, Marshall told them to rush over to acknowledge Slater in his milestone match.
Past and former players have taken to social media to praise Marshall for his selfless act, including Monty Betham, David Mead and Jake Marketo, plus countless fans.
In a match full of drama that featured plenty of errors by both sides, the Ivan Cleary-coached side prevailed after Ben Matulino's pass found Luke Brooks who dived to score the match-winner in the Telstra Premiership round-two encounter and shock a disbelieving bumper Melbourne crowd.
Slater became the 31st player in premiership history to chalk up 300 games a week after his long-time representative teammate Johnathan Thurston achieved the honour in Townsville in the North Queensland Cowboys' win over the Cronulla Sharks.