Taylor was seen by a doctor at the ground and will be monitored ahead of a scan.
Kane Williamson (78) and nightwatchman Jeetan Patel (9) were the not out batsmen.
The initial duel between Vern Philander and Williamson was a highlight. The result? Minimal runs but tenacity; utter commitment versus utter concentration. It's an element to savour across the series.
A solitary television frame saved the New Zealand captain from a run out calamity with Henry Nicholls in the 46th over at 154 for two. Five overs later Nicholls exited for 12 to a blinding snare from Hashim Amla at first slip off Keshav Maharaj.
Williamson's main blips came from edging Maharaj deliveries in front of Amla on 10 and 40.
He received quality support from Raval who reached his third half-century. The milestone was significant against a strong attack and will give him confidence if Taylor is lost for the series.
The hosts took six wickets for 79 to wrench back parity at the start of the day.
Neil Wagner's dismissal of Dean Elgar for his highest test score of 140 summed up their efforts in the opening session.
Elgar looked to pull, but the ball was too quick for him on an unresponsive wicket. Wagner secured the edge and B-J Watling pouched the catch, earning redemption after dropping Elgar on 36.
Watling struggled despite resting a sprained right knee in a three-week lay-off following the Bangladesh series.
He missed a run-out of Philander which could have had South Africa nine-down and facing a half-hour extension before lunch.
The slip cordon, who use the wicketkeeper's positional judgment as a gauge, sometimes seemed set too deep with the lack of bounce from the pitch. One Elgar edge fell short of first slip when the opener was 132.
Wagner competed with energy and toil after getting picked as the second pace bowler ahead of Tim Southee. He finished with three for 88.
Patel got in on the act, dismissing Quinton de Kock for the third successive time in international innings. He flighted the delivery and de Kock ballooned the ball to a diving Wagner at point.
Boult complemented the effort by luring Temba Bavuma into gloving a ball down the legside as he encroached across the crease towards off stump.
We fought hard and got a lot of reward without letting them get too far ahead of the game," Boult said.
"The wicket's relatively slow and I haven't seen it turn too sharply yet."
Bavuma's fifth test half-century added to a fifth-wicket stand of 104 with Elgar. None of his 64 runs were made between point and mid-wicket.
The word from the South African camp was that Kagiso Rabada contracted food poisoning on the opening day, but was getting better by stumps.
