The first leg at Tampines had ended 3-3 with a hat-trick for Aleksandar Duric while the Protectors goals came from Frederic Mendy (2 goals) and Qiu Li.
The second leg in Bishan was not as thrilling with a 0-0 draw but it was no less edgily as neither side could afford to go behind.
Home United then go on to win 4 - 2 in the Penalty Shootout.
Yohann Lacroix (GK), Jufri Taha, Benoit Croissant, Seiji Kaneko, Firdaus Kasman (Shukor Zailan), Ahmad Latiff (Ahmed Fahmie), Akihiro Nakamura, Imran Sahib, Ismadi Mukhtar, Jamil Ali (Aliff Shafaein), Aleksandar Duric (C)
Lionel Lewis (GK), Kenji Arai, Juma'at Jantan, Valery Hiek, Rosman Sulaiman, Shi Jiayi (C), Nor Azli Yusoff, Isa Halim, Frederic Mendy, Qiu Li, Sherif El-Masri (Firdaus Idros)
Lionel Lewis (GK), Kenji Arai, Juma'at Jantan, Valery Hiek, Rosman Sulaiman, Shi Jiayi (C), Isa Halim, Firdaus Idros (Faizal Samad), Masrezwan Masturi (Sufian Anuar), Qiu Li, Sherif El-Masri (Nor Azli Yusoff)