Keane scored his first Prem goal since November 2009 on his Hammers debut.
Boss Grant said: "In the last few games we've scored goals and now we've got someone like Robbie who gets one chance and scores.
"Robbie is a very good player, we're playing good football so it's good for him and good for us."
Victor Obinna also netted twice to sink Blackpool.
The Seasiders are now just four points above the drop zone after six defeats in seven Premier League outings.
But boss Ian Holloway insisted: "I'm not worried at all.
"We haven't been at the bottom all season.
"We're sunshine, we're light and you won't catch me not smiling and enjoying myself.
"We've got to stay strong, work hard and it will turn."