Kim Si-woo became the youngest Players Championship victor after triumphing by three shots on Sunday.
Competing against Team United States at the Cup will be the global team, comprising the top 10 worldwide players in the official world ranking. But a points shift earned Poulter his card, and he took advantage of his opportunity this week.
European Tour legends Poulter and Sergio Garcia entered the final round in contention.
Day, who romped to a four-shot victory in 2016, finished at seven over for the tournament. At 21 years, 10 months and 16 days, Kim is the youngest victor of the tournament referred to as "the fifth major" on the PGA Tour.
Kim will have to do the same unless he can win a major in the next few years.
"I feel like I'm still dreaming that I won this championship", Kim said.
"I've been striking the ball really well for about two or three weeks", Kim said.
Poulter, 20 years older than Kim, knew the goods when he saw the leaderboards.
"But I think I've still got some work to do".
And the Englishman is now relishing the chance to play on the tour where it all started for him back in 1995.
Moreno had a 74 after taking a two-stroke lead into the final round.More news: Demure Melania Trump visits Vatican with black veil, in head-to-toe black
The Spaniard's second shot on the par-five 16th took a kick off the front of the green before heading straight for the cup marking the first time a double eagle has been recorded at the 525-yard hole in tournament history. 13, 14 and 15 to fall out of contention.
"As good as he played yesterday, he's obviously gone out there today and played even better", added Poulter, who shot a 69 to finish T2.
World No. 1-ranked Dustin Johnson matched his best Players score with a 68 and posted his best 72-hole position with a tie for 12th at 2-under.
Kim also drilled his tee shot down the middle of the 18th fairway, setting up one final par - from off the green, of course - to cap a final round that was flawless, at least on his scorecard.
The only thing old about Kim might be his back. Poulter fell short when he missed the cut in his 10th start at the Texas Open, and he figured he would be stuck asking for exemptions the rest of the year.
Poulter has been critical of the Wentworth greens, but with more alterations made to the putting surfaces since last year's event, he is now eager to get going in Surrey. But his smooth swing looked back on point while manoeuvring around TPC Sawgrass' risky layout. He made the most of it by becoming the only serious threat to Kim on the back nine.
An opening 69 raised his hopes.
Kim began the day two shots off the lead shared by Americans JB Holmes and Kyle Stanley - but birdies on the first, seventh and ninth gave him a two-shot lead at the turn.
After dropping two shots during his first nine holes, world No.11 Scott rallied with four birdies on the back side to sign for a two-under-par 70.
"He played like someone that was doing it for five or six years ... like it was just another round of golf", Kim's playing partner Oosthuizen said.