"It is a fantastic achievement, absolutely marvellous," Ferguson said after the 4-1 win.
"Not many players have scored 100 league goals but the service Ryan has given us, quite apart from the goals, is outstanding.
"Ryan is a great character, a great person and a fantastic servant to us all."
On the result the United boss added: "It was a big win. Things can happen in these conditions as they don't suit us."