A Republic side featuring only three of the men who started Saturday's World Cup qualifier in Cyprus, saw off the challenge of Joel Santana's men at Thomond Park in Limerick - courtesy of Lawrence's unstoppable 37th-minute free-kick.
However, the 27-year-old's strike in just his second appearance for his country came distinctly against the run of play - South Africa dominating the first half with an impressive display which lacked only a cutting edge.
Giovanni Trapattoni's understudies defended in depth and with characteristic commitment to ride out the storm in front of a crowd of 11,300 on a night when even the promise of a handful of pre-released tickets for next month's crucial qualifier against Italy failed to fill the stands.
That kind of resilience has become a trademark of Trapattoni's reign - and while his critics bemoan the pragmatism, he continues to get results.
Ireland were much more pro-active after the break, and substitute Leon Best three times went close to extending the lead.
Trapattoni challenged those members of his squad who have largely provided the back-up during the World Cup campaign to make a case for their future inclusion.
For long periods during the opening 45 minutes, the hosts found themselves on the back foot as the excellent Steven Pienaar prompted the likes of Blackburn new boy Elrio van Heerden and strikers Katlego Mphela and Bernard Parker.
It was they who created most of the chances before the break, although goalkeeper Keiren Westwood was never under the kind of pressure he perhaps should have been.
Defender Morgan Gould skied a first-minute effort high over the bar, as did Mphela 10 minutes later, while midfielder Kagisho Dikgacoi saw another effort deflected wide by Stephen Kelly after he surged towards goal.
Pienaar curled a 22nd-minute free-kick just over Westwood's bar, and the Everton man threatened to play Mphela in on several occasions - with central defenders Paul McShane and Sean St Ledger repeatedly at full stretch, particularly when their side was temporarily reduced to 10 men while striker Caleb Folan had four stitches put into a head wound.
But Pienaar was booked for blocking Lawrence's original free-kick after breaking early from the defensive wall - and although van Heerden was similarly premature from the re-take, the Stoke man sent the ball arcing into the top corner.
Ireland returned determined after the break - and with Folan and captain Kevin Doyle pushing their markers ever deeper and Darron Gibson and Keith Andrews tigerish in central midfield.
Santana's side continued with their enterprising approach.
Gibson kept Fernandez on his toes with a 25-yard drive which sailed just wide of the far post.
Best, who had come on as a 59th-minute replacement for Doyle, forced Fernandez into a solid block within two minutes - and Lawrence was devastated to see his follow-up deflected agonisingly wide.
A spate of substitutions sent the game into something of a lull as both sides attempted to re-adjust, but it took a vital close-range block from substitute Darren O'Dea to deny Pienaar an equaliser.
Best three times went close to a second goal inside the final 10 minutes as the Republic finished strongly.