England allrounder Ben Stokes has conceded his troublesome knee is affecting his bowling following his match-winning hundred against South Africa in Southampton.

Man-of-the-match Stokes made a superb century before England sealed a stunning last-ball win in the second one-day international to go 2-0 up with just one to play ahead of Monday's finale at Lord's, reports cricket.com.au

Stokes, bowled just the three overs on Saturday having suffered a knee injury in England's 72-run win in the first ODI at Headingley on Wednesday.

Although scans on the injury were inconclusive, Stokes was deemed in good enough health to play on Saturday, though he conceded afterward the injury was having an impact on his bowling.

"It's just the bowling that's getting affected by my knee," said Stokes.

"Batting, fielding and running around isn't an issue."

The right-armer is set to have a further scan on the knee this week. 

The allrounder, who struck 11 fours and three sixes in 79 balls as he equalled his highest ODI score of 101, told Sky Sports: "It's always nice hitting the ball well and knowing you've got a bit of form behind you."