Johannesburg born and raised Jennings, the 11th man tried as an England Test opener alongside Alastair Cook since Andrew Strauss retired in 2012, was under pressure for his place after a run of low scores - including a duck in the first innings of this match.
If Philander were to play no further part in the third Test, it would be a huge blow for South Africa as he has been their best bowler by far in the Test series.
In his absence the Proteas eventually bowled the hosts out for 353 on day two, Ben Stokes proving a thorn in their side with a crucial 112.
But third slip Dean Elgar could not hold the sharp chance and the ball went for four.
All-rounder Vernon Philander was discharged from the hospital on Saturday morning will bat on day three of the third test against England at the Oval, Cricket South Africa said.
Stokes could not quite cling on, and in Broad's next over South Africa were safely within 200 runs of England's total after a Bavuma cover-drive for four.
Anderson, England's all-time leading wicket-taker, then had South Africa captain Faf du Plessis lbw for one playing no shot.
But a valuable ninth-wicket partnership of 47 ended when Morkel (17) nicked Anderson to Cook at first slip.
Bavuma followed up by driving Roland-Jones for a boundary through mid-on.
But Bavuma was out soon afterwards, with Roland-Jones leading England off the field.
Westley drove the ball beautifully as he quickly asserted himself and he appears to have put himself in front of Gary Ballance who was supposed to return for the final Test in Manchester next week.
England lost Cook shortly after lunch when he was bowled by an excellent delivery from fast bowler Morkel for just seven.