Tries: Cronje 2, Mpeku Cons: Smith 3 Pens: Smith 2
Tries: Gunne 3, Smyth Cons: Gabriel 2, H Byrne
Leinster were edged out 27-26 by the Lions in their opening United Rugby Championship game at Ellis Park on Saturday.
The Irish province tasted defeat despite a hat-trick of tries by Fintan Gunne in the first half, although a late touchdown by Stephen Smyth ensured they left Johannesburg with a bonus point.
Scrum-half Gunne squeezed through the Lions defence after six minutes for the opening score but Erich Cronje crossed for the hosts soon after, Chris Smith kicking the conversion.
Smith extended the home side's advantage with a penalty but Gunne replied for the defending champions, racing over the line for his second try after Josh Ericson broke through the Lions defence and offloaded.
Caspar Gabriel added the extras for Leinster.
Smith added a conversion after Cronje's try to restore the South African side's lead and although Gabriel missed a penalty, Gunne went over and grounded the ball to complete his treble and give Leo Cullen's team a 19-17 advantage at the break.
A Smith penalty moved the Lions in front again by a single point, then in the last 10 minutes Leinster's Dylan McNeice was shown a yellow card.
The Lions took advantage of their superior numbers when Kelly Mpeku went over in the corner shortly before full-time, with Smith adding the conversion.
The hosts suffered a setback when replacement SJ Kotze was sent to the sin-bin late on and Leinster managed a late score when Smyth touched down and fellow substitute Harry Byrne kicked the additional two points.
Leinster continue their tour with an away game against the Sharks next Saturday, while the Lions host the Ospreys.
Lions: Chamberlain, Mpeku, H van Wyk, R Kriel, Cronje, C Smith, Steyn, B Venter, Botha, S Lombard, E Oosthuizen, Delport, Mahashe, Hlekani, F Horn.
Replacements: Brandon, Kotze, R Schoeman, Andrews, Pretorius, Qoma, Cilliers, Adams.
Leinster: Lawlor, T O'Brien, Cooney, Tector, A Osborne, Gabriel, Gunne, Usanov, G McCarthy, Porter, Baird, O'Tighearnaigh, Deegan, Penny, Ericson.
Replacements: S Smyth, Dooley, N Smyth, Deeny, McNeice, Coffey, H Byrne, C Mangan.