Horschel had six consecutive birdies in one stretch and dropped a 27-foot birdie putt on the 72nd hole to win the Zurich Classic of New Orleans. It was the first professional win for Horschel, a 26-year-old who turned pro in 2009.
That also boosts his world ranking to No. 49 after starting the week 91st.
Rumford, who won the Ballantine's Championship in South Korea, makes a bigger gain in the rankings, going from 253rd to No. 122. He made eagle on the first playoff hole Sunday for his first European Tour title since September 2007.
Brandt Snedeker is sixth, with an average of 6.30, and Louis Oosthuizen, at 5.84, is No. 7. Graeme McDowell remains eighth with an average of 5.50, with Steve Stricker (5.44) and Matt Kuchar (5.36) completing the Top 10.