United required a helping hand en route to claiming a seventh straight success in the league, and an 18-point lead at the summit, with a Titus Bramble own goal seeing them to a narrow 1-0 win at the Stadium of Light.
Sunderland, who are scrapping for their lives towards the foot of the table, made life difficult for the Red Devils during a spirited second-half display and Ferguson admits his side had to dig deep to get over the line.
He told Sky Sports: "It was a battling performance by the players. We picked up two or three injuries along the way and it was courage that got us through in the second half. It means we will go into the Man City game with at least a 15-point lead.
"The first half we did well, second half we give credit to Sunderland because they gave it a real go. I thought we had lost David de Gea for a moment, he was out for a few minutes, but he got up and has played a really great part for us.
"I think the players have galvanised themselves - the team spirit, the concentration, the focus in every game. That's 25 wins in 30 league games, which is a record. That's all down to the efforts of the players."
United also collected a sixth successive clean sheet on Wearside, much to the delight of Ferguson who saw his side ship an uncharacteristic amount of goals at the start of the campaign.
He added: "The concentration is much better. Earlier in the season we were losing goals but we have got defenders back - Chris Smalling, Phil Jones coming back helps, Jonny Evans, Rio (Ferdinand) and Vida (Nemanja Vidic). Your selection, two from those five, makes it much easier for us."