Ireland hand South Africa sixth straight defeat
The winger found the top corner with a perfectly curled free kick on 37 minutes to give Giovanni Trapattoni's second-string side a 1-0 victory in an otherwise uneventful match at the Munster rugby home of Thomond Park.
The Italian made eight changes from the team which won 2-1 in Cyprus on Saturday to push Ireland towards at least a playoff position in qualifying for next June's finals.
The lively Lawrence came close to making it 2-0 in the second half as Joel Santana's South Africans failed to turn periods of decent possession into any serious chances.
Ireland, lying a point behind world champions Italy in qualifying group eight, will hope the leaders slip up against third-placed Bulgaria on Wednesday before they travel to Dublin for the penultimate fixture next month.