Ferdinand conceded a penalty but saw his side go three points clear in the Barclays Premier League table thanks to goals from Wayne Rooney and Javier Fernandez.
Ferdinand told Sky Sports 2: "You've got to win games. I don't care how we win. The three points is all that counts.
"You've got to dig deep in these games and these are the type of games you can make up a lot of ground in the league."
Ferdinand added: "Credit to West Brom, they played some good football. They are not scared to pass the ball around."
Rooney opened the scoring when he headed in Patrice Evra's cross on three minutes but James Morrison equalised with a long-range shot.
United survived when referee Chris Foy turned down obvious Baggies penalty claims after Gary Neville sent Graham Dorrans flying.
West Brom striker Peter Odemwingie later fired a penalty wide after Ferdinand had fouled Jerome Thomas.
Hernandez secured the points when he headed in after 75 minutes.
United manager Sir Alex Ferguson admitted his side had struggled against West Brom.
"It was a really tough game on a greasy pitch," he told Sky Sports 2.
"It's a massive result for us today. Over the years we've had to battle out games and we have had to do that today.
"In the second half we started to play a bit better. We had to make changes with one or two injuries."
Ferguson admitted he thought Neville had conceded a penalty, but only after he had seen the incident for a second time.
He said: "I thought it was a penalty. I thought at the time Gary got it (the ball) but when I saw the replay he got the outside of the player's leg."