In 2005, Sim turned professional at the end of the year. He played on the
Nationwide Tour in 2006, and qualified for the
PGA Tour by virtue of a 19th-place finish on the end of season money list, aided by a win at
PalmettoPride Classic. After a late start to the 2007 season, caused by a
stress fracture of the spine, he finished 169th on the PGA Tour money list. He was granted a medical extension for 2008, but failed to win enough money in five events to retain his place on the PGA Tour, and he returned to the second tier Nationwide Tour. In April 2009, Sim's bid to return to the elite tour got off to a good start when he secured his second career victory at the
Stonebrae Classic, finishing six strokes clear of the field. The following week he finished in second after losing in a playoff to
Patrick Sheehan, and then in May he won the
BMW Charity Pro-Am in a playoff over
Fabián Gómez. Sim played with
Tiger Woods during the final round of the
2009 U. S. Open and finished in at tie for 18th. He was invited a month later by the PGA to play in the
2009 PGA Championship at
Hazeltine National Golf Club where he finished T51. Sim won the
Christmas in October Classic to earn an automatic "battlefield promotion" to the PGA Tour. The victory was his third Nationwide Tour win of 2009 and his fourth overall. With the win he also set the Nationwide Tour single season money title, earning well over half a million dollars. He was one of the top 50 players in the
Official World Golf Rankings in 2009, which earned him entry into the
2010 Masters Tournament; he later withdrew from the tournament due to injury. He also won the
PGA Tour of Australasia Order of Merit in 2009. Sim performed moderately on the PGA Tour in 2010, with the highlight of his season being a T-2 at the
Farmers Insurance Open. He comfortably retained his card by finishing 65th on the money list. In 2011 Sim could not follow up his PGA Tour rookie season and went back to the Web.com Tour in 2012. A string of injuries limited Sim after the 2011 season and he played sparingly on the
PGA Tour of Australasia,
Korean Tour,
OneAsia Tour, and Web.com Tour. ==Amateur wins==