New Zealand opener Martin Guptill struck a four off the final ball of the match en route to a quickfire century, resigning South Africa to an eight-wicket defeat in Sunday's truncated second Twenty20 International in East London.

A fixture reduced to 19 overs per side by a floodlight failure at Buffalo Park ultimately treated the 15,000-strong sellout crowd to a genuine spectacle, with Guptill's heroics levelling the three-match affair ahead of Wednesday's series decide.

Hapless at Kingsmead, the tourists put in a much tighter effort in the field, with captain Brendon McCullum's decision to bowl first after winning the toss proving vital. The Proteas struggled with a damp ball during the opposition's pursuit, coughing up a slew of full tosses, which Guptill and company were reasonably quick to cash in on.

The hosts' total was built on the back of half-centuries from opener Henry Davids and captain Faf du Plessis, who were particularly severe on a visiting attack lined with bits and pieces all-rounders. The left-handed David Miller, too, cherished the substandard nature of the bowling, launching into a 33-run cameo that spanned a mere 18 deliveries.

The Black Caps took a lot of confidence from fast bowler Doug Bracewell's three wickets in the last over of the innings, though, which eventually translated to success with the bat - almost entirely finalised by Guptill's gargantuan effort.

Having recovered from the bout of gastroenteritis that ruled him out of the first T20I, Guptill promptly resumed his lead role at the top of the knock. In partnership with fellow opener Rob Nicol he was outstanding, in cahoots with skipper Brendon McCullum he was simply fantastic.

Key to Guptill's success was his ability to strike the ball straight, through its line and hard over the fence for all of six sixes. Nine boundaries, meanwhile, complemented his epic vigil.

Very severe on debutant spinner Aaron Phangiso, who copped expensive figures of none for 42 in four overs, Guptill's knock was arguably the most well constructed of the year. McCullum, who eventually perished for an uncharacteristically timid 17, played second fiddle throughout their 73-run alliance in one delivery more than seven overs.

Seamer Rory Kleinveldt was entrusted with the final six balls of the cliffhanger. Under much more pressure than that brought by his match-winning performance in Durban, the right-armer failed to rise above adversity. Conceding just seven runs from the first five, Kleinveldt ultimately coughed up a rank full toss for Guptill to slice through the covers - and with that the nail-biter was decided.

Utterly jubilant in his celebration of the winning runs, and only T20I cricket's ninth century, Guptill was proudly named Man of the Match for his unbeaten 101 from just 69 deliveries.

South Africa, however, were left to contemplate an off day in the field, which saw the otherwise reliable Robin Peterson spill a chance in the point region and the oft-trusty Farhaan Behardien shell an opportunity at deep backward square-leg. For McCullum and company, it was sweet relief - and a certain turn up in the books at the start of a tour they were expected to flounder through.