The Black Cats recorded a 4-1 at the DW Stadium and ensured they moved into the top half of the Premier League for the first time this season as James McClean scored his first goal
The Black Cats picked up the comfortable win following goals from Craig Gardner, James McClean, Stephane Sessegnon and David Vaughan, while Hugo Rodallega scored Wigan’s solitary strike.
Sunderland are now unbeaten in their last four matches and have recorded wins against QPR, Manchester City and now Wigan.
“The players don't feel that they can be beaten at the moment. I think they are enjoying winning football matches," O'Neill told reporters.
"I'm delighted with the spirit of the team. They feed off each other and it was a magnificent performance."
Despite picking up a smash-and-grab win at the Stadium of Light against Manchester City on New Year’s Day, O’Neill believes this latest victory is the most impressive since joining the club.
"I thought it was our best win since I've been here for every reason under the sun,” he declared.
"The players were out on their feet against Man City a couple of days ago - and had a day less to prepare - but they summoned energy and courage that was fantastic.
"There were one or two games, before I came, when Sunderland didn't have luck.
“We've had a wee bit of fortune. It's a terrific run for us and has given us a bit of breathing space."
The former Aston Villa boss also reserved some special praise for two players in particular after McClean put in a solid display and Jack Colback impressed, despite playing out of position.
He continued: "It was a wonderful performance by McClean, and Colback was absolutely fantastic.
"Colback has gone in and played left-back a couple of times and adjusted brilliantly."