Cook and Bairstow lift England
Alastair Cook and Jonny Bairstow kept England in reasonable health, after the loss of two wickets for one run in Wednesday's final NatWest Series match against South Africa at Trent Bridge.
England faltered to 24 for two in the fifth over, after choosing to bat first on a glorious afternoon for this day-night fixture.
But after 15 overs, opener Cook and Bairstow guided them to a more reassuring 63 without further loss.
Victory would not only finish a sequence of 13 wins from 14 completed one-day internationals this year for Cook's world number one team, but would also wrap up an eighth successive home series victory.
England made an encouraging start until Ian Bell missed a delivery that came on with the arm from Robin Peterson and was lbw pushing forward, Simon Taufel's decision confirmed after the batsman invoked DRS.
Ravi Bopara, pushed up to number three in the absence of the injured Jonathan Trott, is enduring a nightmare run of form.
His troubles continued when Steyn got one in the ideal place, and Bopara got a thin edge to be caught-behind for single figures for the third successive time in this series.
This was also his second duck in those three innings, and put added pressure on new batsman Bairstow - called up for his first one-day international cap since last October.
The young Yorkshireman had one minor moment of fortune on 10 when wicketkeeper AB de Villiers could not cling on to a half-chance, off an inside edge at Steyn.