In June 2015, he became the first SMU Mustang to win the NCAA individual championship, recording a score of 280 (−8) to win by one stroke.[3] In August, he won the U.S. Amateur title, defeating Derek Bard 7 & 6 in the 36-hole final. He became the fifth player to win both the NCAA and U.S. Amateur titles in the same year, joining Jack Nicklaus (1961), Phil Mickelson (1990), Tiger Woods (1996), and Ryan Moore (2004).[2]
On June 3, 2018, DeChambeau won the Memorial Tournament in Dublin, Ohio, in a sudden-death playoff against Kyle Stanley and An Byeong-hun, after the three finished regulation play tied at −15. After Stanley bogeyed the first hole of sudden death, DeChambeau then proceeded to win with a birdie on the second hole, giving him his second win on the tour.[16]
Lowry started his youth career with Australian club ECU Joondalup. He signed for Aston Villa in February 2005 along with fellow Australian Chris Herd.[3] Lowry made nine appearances for Aston Villa Reserves in the 2006–07 season, mainly coming near the end of the campaign. Lowry was also part of the squad that won the HKFC International Soccer Sevens in May 2007. In June 2007, Lowry signed a 12-month deal to his contract.

Lowry was the 2007 Irish Amateur Close Champion, defeating Niall Turner 4 & 3 in the final.[5] While still an amateur in May 2009, he won The Irish Open on the European Tour, defeating Robert Rock on the third hole of a sudden death playoff. The win, on his tour début, made him just the third amateur to win on the European Tour,[6] following Danny Lee earlier in the 2009 season, and Pablo Martín in 2007. Lowry shot a 62 to equal the lowest ever by an amateur on the circuit and led from the second round onwards.[7]
In the 2013–14 season, Lowry suffered a minor thigh strain in the club's pre-season friendly.[35] Despite this, Lowry remained in the first team under the new management of Steve Lomas until he received a straight red card after a foul on Will Hughes, in a 5–1 loss against Derby County on 14 September 2013.[36] After serving a three match ban, Lowry remained on the bench without playing for four matches[37] Lowry made his first team return on 2 November 2013 when he came on as a substitute for Scott Malone against Burnley. However, his return, after spending two months without playing, was a disastrous when he scored an own goal, which saw Millwall drew 2–2.[38] After this, Lowry was out of the first team, demoted to the substitute bench between mid-November and mid-December until he made his return on 26 December 2013, in a 4–0 loss against Watford.[39] On 28 January 2014, Lowry was sent-off for the second time this season in the late-minutes against Sheffield Wednesday after fighting with Giles Coke, who also was sent-off as well, with both side drew 1–1.[40] After serving a four match ban,[41] Lowry was in the first team throughout February and March until he suffered a foot injury that kept him out for the remainder of the season.[42] Lowry went on to finish the 2013–14 season, making twenty-two appearance.
Lowry made his professional debut in the 2009–10 UEFA Europa League in an away fixture at Rapid Vienna.[4] On 17 September 2009, Lowry signed a three-month loan deal with Football League Championship side Plymouth Argyle.[5][6] Lowry made his Plymouth Argyle debut on 19 September 2009, playing 90 minutes, in a 3–1 loss against Newcastle United.[7] He played 13 league games for Plymouth during his loan spell, where he impressed many and was recalled by Villa who required Lowry's services as cover after some injuries to defenders.[8]
Lowry elected to turn professional the week after his Irish Open triumph, meaning that he would miss out on the opportunity to play in the Walker Cup in September 2009.[11] He made his professional début on 28 May at the European Open, where he shot 78 in the first round to end the opening day almost at the back of the field, and went on to miss the cut following a second round 73.[12] 
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