"Pull more than the other team, and you will win."
Translation:Tiru pli ol la alia teamo, kaj vi gajnos.
You are right. Venki is a transitive verb. It has got a more absolute meaning than gajni. Therefore the intransitive verb venkiĝi means just the opposite: to be defeated.
gajni – to win, to earn
malgajni – to lose
venki – to defeat, to prevail, to be victorious
venkiĝi – to be defeated
malvenki – to go under