Shane Long opened the scoring in Republic of Ireland's 3-1 win in Moldova, but was forced off with an injury in the second half.
Saints striker Long latched onto a Wes Hoolahan through pass to slot home inside the opening three minutes of the World Cup qualifying match.
He was forced off shortly after the hour mark, with the score at 1-1, following Igor Bugaev's equaliser on the stroke of half-time.
Despite having to leave the action, Long was able to celebrate a win, as James McClean netted two quick-fire goals to help the Irish follow up Thursday's 1-0 victory over Georgia.
Ireland now have seven points from their opening three games on the road to the 2018 finals in Russia, and they will visit Austria for their next qualifier, in November.