John O'Shea believes Sunderland recruited well in January, with fresh faces having settled quickly in new surroundings.
Black Cats boss Gus Poyet was able to make five additions to his squad during the winter window, with Liam Bridcutt, Marcos Alonso, Oscar Ustari, Santiago Vergini and Ignacio Scocco drafted in to the Stadium of Light.
The quintet have all been offered early opportunities to impress, and none have looked out of place on the Premier League stage.
Sunderland need them to hit the ground running, as they scrap for top flight survival, and O'Shea believes Sunderland are reaping the rewards for going about their business in the right manner.
He told the Echo: "The manager knew all about the players he brought in in January.
"That was an important thing for him. He wanted players who could settle in quickly because of the position we're in.
"We needed to add quality to the squad too, to increase the competition, and I think he's done that.
"If you have competition, that will always be the key to a successful team."
O'Shea has played his part in helping Argentine new boy Vergini to find his feet, having partnered him at centre-half in last weekend's FA Cup win over Southampton, and the Irishman believes the on-loan Estudiantes defender will go from strength to strength as he masters the English game and language.
He added: "It will be the manager's call when Wes (Brown) comes back (from suspension), but Santi has obviously done brilliantly.
"For him to come into these games in the way he has, has been fantastic.
"He's very, very comfortable on the ball coming out from the back and he's a no-nonsense defender when he has to be too.
"He has enough English to get by on a football pitch, but he'll grow in confidence from the game against Southampton. So will Oscar, while Nacho's fitness will improve."