The Black Cats suffered their first defeat since returning to the Barclays Premier League as they were brushed aside by Wigan at the JJB Stadium.

Emile Heskey gave the home side a 19th-minute lead and Wigan sealed the points after Sunderland gave away two penalties in nine minutes midway through the second half.

Denny Landzaat and then Antoine Sibierski converted the spot-kicks to give Wigan their second win in four days and send them top of the Premier League table.

Keane, however, was left to reflect on the wisdom of his team selection as his defence struggled to cope with Heskey and Sibierski throughout, while Dwight Yorke and Anthony Stokes returned to the starting line-up only to be substituted at half-time.

"We've got to learn, and we've got to learn fast," said Keane. "But some of the lads have been here before and clearly they haven't learned.

"I do take full responsibility; I'm the one who's picking the team.

"There's a fine line between loyalty and stupidity, and no doubt I've been stupid - it won't happen again.

"I think, last season, the defeats at home to Cardiff and at Preston taught me a lot about different players and different characters - who you think's going to be on the journey with you," he added.

"You tend to find out more about your players when you lose than when you win, and I found out a hell of a lot here, let me tell you."

Keane forged a fine team spirit at Sunderland last season as the Black Cats repeatedly came from behind in their charge to the Coca-Cola Championship title.

And although they managed to fight back and claim a 2-2 draw at Birmingham in midweek, Keane knows the Wearsiders cannot afford to continue giving their opponents a head-start if they wish to establish themselves in the top flight.

"There was no surprise about Wigan," he said. "They worked extremely hard, they're a big, strong, physical team, but we helped them along the way, especially with the two penalties.

"We gave ourselves mountains to climb last year in the Championship by going behind in lots of games and coming back with late goals, and we did it again at Birmingham, but you can't keep doing that, not in the Premiership - a blind man can see that."

Keane has already spent $67million in a bid to add enough depth and quality to the Sunderland squad to keep them in the Premier League, but with Carlos Edwards, Grant Leadbitter and now captain Dean Whitehead out injured, there could be more signings before the transfer window closes.

"We were looking at that anyway, likes lots of clubs, but that's not a knee-jerk reaction to this defeat," Keane said. "We definitely need a bigger, stronger squad.

"With Deano getting injured and Grant missing, it gives other players an opportunity, and some take that, some don't."