By Andrew Both
"To finally win over here, it means everything," Poulter told reporters. "I'm just so happy to finally win on American soil."
"I was very comfortable on the course today. I felt in control of my game all week. I don't know if there was any given point where it was going to be my week (but) I just felt very calm."
The win gave Poulter a $1.4 million winner's check and propelled him to fifth in the world rankings, but the Briton said he would have to hold off on the celebrations.
"I didn't quite say it was just me and Tiger (but) I just felt that if I could deliver what I believed I could, then I could put myself in a good situation and I've certainly done that over the last 18 months and I've certainly been able to deliver on that today."
Poulter dominated most of the 36-hole final, trailing for only one hole early before taking the lead for good at the seventh. He was two-up after 18 holes and never led by less during the second round.
"Ian played great stuff," Casey told reporters. "You're probably going to write Casey played rubbish but you have to realize Ian played excellent golf.
"I think he kept it in play on every single hole around here, and made a lot of clutch putts. He's putting very, very well."
Poulter, 34, has employed science to hone his putting, using a new system that charts the exact break on the greens.
"I don't know if I want to give the secret away but I've done a lot of homework on the greens this week," he said.
The Englishman also caught a lucky break when Casey's semi-final against Camilo Villegas stretched into Sunday morning after the two were deadlocked after five extra holes late Saturday.
Though Casey needed only one more hole to dispatch Villegas Sunday, he appeared drained and made a scrappy start to the final.
"I was just amazed they were on the course three hours after I'd finished," said Poulter. "That might be one of the factors why I've come through the way I have today."
Added Casey: "I feel mentally tired but I'm not going to make excuses. There were a lot of shots I wanted to pull off and didn't."
In the match for third place, Colombian Villegas bounced back from his semi-final disappointment to beat Spaniard Sergio Garcia 5&4.
(Editing by Ian Ransom)