Valletta opened a four-point gap on Hibernians after edging Balzan 2-1 in a hard-fought clash.
Needing a win to keep top spot ahead of their potentially descisive final-day match against Hibs, who meet Birkirkara tomorrow, Valletta had Michael Mifsud to thank for the three points as the veteran striker hit a late winner after Balzan had equalised close to the hour mark.
Valletta were the more creative side for much of the opening half but they only had one goal to show for their efforts.
It came on 13 minutes when Federico Falcone capitalised on a half-clearance from Balzan to drill a powerful drive past Ivan Janjusevic, the Balzan goalkeeper.
Earlier, Janjusevic had been nearly deceived by Claudio Pani's long-range drive but the Balzan goalkeeper just managed to tip the ball over the bar.
Valletta had a great chance to increase their lead when Rafael Ledesma slipped a a perfect pass to Falcone but the Argentine striker blasted high from close range.
Late in the first half, Jhonnattann was sent clear by Ledesma but he drove wide.
Spiteri sent on Bojan Kaljevic for Da Silva Souza at the start of the second half.
Kaljevic threatened to make an instant impact but hit wide after connecting with Justin Grioli's pass from the right.
Balzan improved. Kaljevic headed over from Grioli's cross but Mifsud should have eased Valletta's nerves when put through by Jhonnattann but the Malta captain's central shot was stopped by Janjusevic.
Balzan levelled on 59 minutes. Pedrinho's long ball sailed past the dithering Ryan Camilleri and Kaljevic nipped in to hit home.
Jhonnattann headed over from Calistus's cross with 12 minutes left but three minutes later, Valletta regained the lead.
Falcone's excellent pass released Mifsud who ran past the backtracking Balzan defenders before riufling past Janjusevic.
Mifsud then drifted into the box from the right before teeing up Jhonnattann whose flying volley came off Serrano.
Federico Falcone was named BOV player of the match.
VALLETTA - H. Bonello, F. Falcone, R. Ledesma (A. Nafti), J. Benites (R. Romao) , R. Briffa, M. Mifsud (L. Cremona) , I. Azzopardi , U. Calistus, C. Pani, R. Camilleri, J. Caruana.
BALZAN - I. Janjusevic, J. Grioli, P. Fenech, S. Bezzina, P. Dos Santos Calcado, C. Brincat, A. Effiong, A. Da Silva Souza (B. Kajlevic), L. Micallef, E. Serrano Valero, D. Grima.