Dom Sibley said he enjoyed "one of the best days" of his life as he nudged his way to a maiden Test century in the shadow of an astonishing innings by Ben Stokes which put England in a strong position to win the second Test and square the series against South Africa.
Set a world record 438 to win, South Africa were 126 for two at the close on the fourth day at Newlands.
Stokes effectively put the game beyond South Africa's reach by slamming 72 off 47 balls.
Sibley, who made 133 not out, said he had a sleepless night on Sunday thinking of the 15 runs he needed to advance from his overnight 85, but that batting with Stokes took the pressure off him.
"It made it really easy for me to go at my tempo," said Sibley. "When he was whacking it everywhere and I was nurdling it around and playing and missing it was nice that at the other end he was doing the scoring."
England's batting was in dramatic contrast to their effort on Sunday when they ground their way to 218 for four off 79 overs.
Sparked by Stokes, they added another 157 runs in the morning session before declaring five overs after lunch on 391 for eight.
Sibley said he was in awe of the way Stokes and Jos Buttler, who hit two sixes in making 23 runs off 18 balls, were able to play aggressive pull shots off fast bowlers like Anrich Nortje.
"I'm usually just ducking –- and Stokesy was reverse-sweeping fast bowlers. They are incredible talents. It was great fun to watch them from the other end."
The tourists had to work for 56 overs to take two South African wickets.
Opening batsman Pieter Malan, making his Test debut, scored 63 not out and shared half-century partnerships with Dean Elgar (34) and Zubayr Hamza, who was caught behind off James Anderson in the penultimate over of the day for 18.
Elgar's dismissal, also caught behind by Buttler despite an unsuccessful review, gave Joe Denly his first Test wicket.
Sibley said England would seek to take a few wickets with an old ball which showed signs of reverse swing late on Monday, then strike with the second new ball, which should be available before lunch on the final day.
South Africa, meanwhile, will seek to bat out the last day on a pitch which batting consultant Jacques Kallis, the country's all-time leading Test run-scorer, said had "flattened out", although it was offering some help to spin.
"I've seen some crazy things happen," said Kallis. "We've just got to bat normally and face as many balls as we can. As long as we make England fight for our wickets and don't give away soft ones, who knows what can happen."
Kallis praised the batting of Malan, making his Test debut at the age of 30 after scoring more than 10,000 runs in first-class cricket.
"He's got a lot of cricket under his belt. He's got a good technique and played the situation perfectly. He's very organised and he's a fighter. I was very impressed with his mental capabilities."
South Africa chose not to take the second new ball when it was due after one over at the start of play.
"We knew Stokes was going to come out to play," said Kallis. "With the rough there for (left-arm spinner) Keshav (Maharaj) bowling to the left-hander and the ball a bit soft, we thought hopefully one would misbehave if he tried to go early on."
He said the fact that fast bowler Nortje was ill at the start of play was another factor.
The tactic backfired, however, as 28 runs were added in five overs before the new ball was taken, including sixes by Stokes off Dwaine Pretorius and Maharaj. When the new ball was taken Stokes continued to attack almost every ball he faced.