Sliema suffered more than expected to have the better of Sirens, and needed to wait until 19 seconds from the end to open up a two-goal lead that ensured them of victory.
Jacob Sciberras scored against his former club to end the game with a 5-3 score.
The match was tight right from the start, with Suirens defending bravely and always keeping in touch with their opponents.
But Sliema's experience came in handy in the latter stages of the match for them to secure victory.
In the other match, Marsaxlokk beat Otters 10-6.
Sirens Mecca Marin 3
Sliema Frank Salt 5
(2-3), (0-1), (1-0), (0-1)
Sirens: J. Parnis, J. Ciantar, K. Erdogan (1), G. Melillo, J. Zerafa Gregory, T. Said, L. Falzon (1), I. Riolo, J. Napier, M. Cutajar, M. Sciberras, M. Azzopardi (1), O. Gauci, G. Farrugia, G. Sammut
Sliema: N. Grixti, J. Gabarretta, L. Galea (1), J. Sciberras (1), M. Meli, B. Cachia, M. Spiteri Staines (3), J. Cutajar, J. Brownrigg, Z. Mizzi, N. Bugelli, Z. Sciberras, C. Cutajar, E. Schembri
Referees: Alex De Raffaele, Raffaele Colombo
Otters Nivea 6
Marsaxlokk Brown’s 10
(1-3), (0-2), (1-2), (4-3)
Otters: M. Xerri, C. Spiteri Debarro (1), R. Caruana, M. Lanzon, E. Meli (1), L. Gialanze (1), K. Scicluna, I. Azzopardi, D. Dimech, D. Zahra (3), M. Farrugia, S. Xerri, D. Spiteri, M. Caruana Baluci, L. Dimech
Marsaxlokk: R. Coleiro, J. Rizzo Naudi, M. Martellacci (2), J. Portelli, T. Agius (3), L. Saliba, J. Galea, K. Cremona (1), S. Micallef (2), M. Pace, M. Cacici, O. Zammit, B. Lanzon (2)
Referees: Peter Balzan, Aldo Rovandi