Smith, who had replaced an impressive Johan Goosen minutes earlier, placed the kicking tee just inside his half and the ball snuck over the crossbar, but they all count and the Vodacom Bulls took the lead with less than five minutes left.
Goosen, on debut for the Vodacom Bulls, earlier made a sizeable mark on the game. The men from Pretoria were trailing by 14-0 at the break, but two interventions by their starting flyhalf saw Keagan Johannes race in for a try under the sticks and a minute later, Johan Grobbelaar scored on the same spot, both converted by Goosen to draw scores level in a flash.
After 65 minutes of to and fro and some glimpses of class, Goosen stepped inside some defenders and fed his halfback partner who ran in untouched.
The Johannes try gave some meaning to the game, and certainly sparked the interest of Goosen, who sniffed out the opportunity like an experienced pivot.
From the restart, Goosen again saw a gap in the tiring SA 'A'-side defence and put Muller Uys through at full speed. The big flanker ran strongly and the Vodacom Bulls distributed nicely out to the wing, where FC du Plessis found himself trapped against the touchline, but a clever kick infield was gathered by Grobbelaar who ran in without a green jersey in sight.
Goosen kicked the conversion and suddenly it was all square with 10 minutes to play, which is how it stayed until Smith landed the bomb that earned Jacques Nienaber a first defeat in green and gold as head coach.
The match reminded much of a typical SA derby in the early stages, although SA 'A' opted for lineout drives and not kicking to the poles. The Bulls repelled the first one, but conceded a penalty in the process and from the next drive erred again, but managed to stop the drive (illegally) again. This time SA 'A' opted for a scrum, but the men from Pretoria were rewarded a penalty when Coenie Oosthuizen lost his bind.
That respite was short-lived however as SA 'A' caught the Vodacom Bulls defence napping, with Cobus Reinach delivering a sniping break to hand Aphelele Fassi an easy run in. Elton Jantjies converted from right in front to hand his team a 7-0 lead 12 minutes in.
The Vodacom Bulls came with a ferocious charge though and from the kick-off enjoyed a long spell inside the SA 'A' 22. They kept pegging away at the A-side's defence and got some sort of reward then Wandisile Simelane was binned for going offside.
It did not deliver any points though and the men in green and gold could escape without conceding.
Both teams showed little ambition to carry the ball in the early stages, but the game opened up midway through the first half, with both sides starting to use their backs to gain territory. Tight defence reigned though and it became a slugfest of rucks and big hits.
The second try of the match came just before halftime, with Simelane getting his five pointer. The midfielder had to thank a number of good runs by a rash of ball-carriers, as the SA 'A'-side seemed to find some patience on attack and a willingness to work off the ball.
They stretched the Bulls defence till Simelane could eventually just drop over the line without a defender in sight to stop him.
The second half, bar some exciting runs by Rosko Specman on the wing for SA 'A', will be remembered for the Vodacom Bulls' comeback.
South Africa 'A' 14 (14) - Tries: Aphelele Fassi, Wandisile Simelane. Conversions: Elton Jantjies (2).
Vodacom Bulls 17 (0) - Tries: Keagan Johannes, Johan Grobbelaar. Conversions: Johan Goosen (2). Penalty goal: Chris Smith.