Seigle himself delivered the killer-blow on the never-say-die Sta. Lucia squad with his final basket in the long night, making it 96-94 with 17.8 seconds left in the clock.
Raheim Brown tried to salvage the game with a three-point attempt in the ensuing play but missed, allowing the Beermen to escape with their third win in four starts.
Dorian Peña, fouled by Dennis Espino at the buzzer, scored a free throw for the final tally.
The Beermen survived the fierce-fighting Realtors despite losing import Chris Burgess to fouls with a minute to go in regulation play.
Seigle almost single-handedly carried the fight for the Beermen but nearly threw it away with a crucial error in the closing seconds of the regulation period.
The Realtors failed to buy a basket in the last 24 seconds as the game went into the first overtime.
Paolo Mendoza rifled in a trey in the last two seconds of the first overtime to force the second extension play.
Hitting their stride in the second quarter, the Realtors wiped out a 21-13 deficit and took a 42-37 advantage at halftime.
The Realtors outscored the Beermen by 13, 29-16, in the second period as they shot 53 percent from the field as against San Miguel’s woeful 22-percent clip.
Marlou Aquino tied the count at 24 on a free throw with time down to 7:07 and himself broke the standoff with a strong drive moments later.
Starting the final half like they did in starting the game, the Beermen wheeled back into the lead at 48-47 with their searing charge punctuated by a booming triple by Dondon Hontiveros.