[1] Yap started off his S.League career with Balestier Khalsa in 2009, before moving on Gombak United in 2010.

He moved to Woodlands Wellington FC in 2012 and made his debut for the Rams in their match against Tampines Rovers shortly after passing his beep test for the club.

He scored his first professional goal of his career while playing for Woodlands Wellington during a 3–1 loss to Tampines Rovers in a preliminary round match of the Starhub League Cup on 27 July 2012.

In 2018 FA Cup third-placing match, Aloysius scored a hat trick to give Singapore Arm Forces SA (SAFSA) a 5-0 victory over Admiralty CSC .

[3] While working as an OCBC Premier Banking relationship manager,[4] Aloysius was one of the three nominees for 2019 National Football League Division One Player of the Year.