THOUSAND OAKS, Calif. -- The popularity and success of Tiger Woods over the years has often been credited with the dramatic rise of purses on the PGA Tour.

Now he's contributing to purses directly.

Woods confirmed Saturday at Sherwood Country Club that he personally "bridged the gap," to help the World Challenge presented by Northwestern Mutual meet its operating costs. Woods would not verify the seven-figure amount, but The Associated Press reported it to be $4 million.

"I'm not going to tell you the exact amount, but it's a good number," Woods said in an interview after shooting a third-round 69 that put him five strokes back of tournament leader Graeme McDowell.

"What's important is that if it wasn't for this tournament, we wouldn't have the success with the foundation. The Learning Center (in nearby Orange County) would not have happened. We wouldn't have gained the awareness that we have now.

"There have been so many kids that we have helped, just because of this event. It's important to me, to the foundation. This is what got us on the map."

This tournament began in 1999, and was inspired in part by Woods' late father, Earl. Although he now has an affiliation with the AT&T National in Washington, D.C., and the Deutsche Bank Championship near Boston, this is the tournament that Woods holds dear, said his agent, Mark Steinberg.

"He started this one with his father,'' Steinberg said. "And he didn't want to see the foundation take a hit in order to stage the tournament."

Since its inception, the World Challenge has raised more than $25 million for the foundation. It helped Woods start his Learning Center -- to which he contributed the first $5 million -- as well as other endeavors in other parts of the country.

Not widely known, Woods has been contributing his prize money from the World Challenge, the AT&T National and the Deutsche Bank Championship to the foundation. He won the World Challenge last year and the AT&T over the summer, victories that were worth more than $1 million each. He's contributed more than $14 million of his prize money alone over the years.

"It's kind of a running joke with the foundation," Woods said. "You better win the tournament because we're kind of counting on this amount of donation. So it's fun."

The purse for this week's tournament is $4 million, with $1 million going to the winner and $120,000 to the last-place finisher in the 18-man field. But it costs far more than that to put on a tournament. The event is televised by NBC, and the way PGA Tour events are structured, production costs and a good bit of advertising is covered by the title sponsor.

Without one, those fees must still be paid, or the tournament could not exist. The total outlay for a regular PGA Tour event is typically in the $6 million to $7 million range per year. Greg McLaughlin, president and CEO of the Tiger Woods Foundation and also the tournament director, said a title sponsor likely would pay about four times more than what Northwestern Mutual is contributing this week.

Steinberg, said a potential title sponsor fell through in the fall, leaving event organizers scrambling.

"That's exactly what happened," Woods said. "The title sponsor unfortunately fell through. This is important for us."

The tournament would have been forced to dip into reserve funds or possibly not be played if it were not for Woods' support. And while the proceeds from the event are helpful, Woods said the exposure it brings to his charitable causes are also reasons for wanting to keep it going.

"It's both, fundraising and awareness," he said. "This provides us a platform to show people how we are helping kids. This is where it all started. We are a foundation, yes, but people really didn't understand what we were trying to do. Once we built the Learning Center, because of this event, that allowed us to do that.''

McDowell, who finished second here in 2009 and won the event in 2010 (and made $2 million in prize money), said the players were not aware of Woods' generosity in helping the tournament this week.

"That's a hugely honorable thing to do," McDowell said. "He already gives back so much to the game. He's a huge reason why we're playing for so much money around the world. These TV contracts, all these spectators, it's awesome. And it's a really cool thing of him to do."