When bad light ended play, South Africa were 250 for eight in their second innings. They also scored 303 in their first innings for an overall lead of 283 on a pitch, which has helped bowlers throughout.
Australia will require more than the 270 they scored in the first innings if they are to complete a 3-0 series sweep.
"There's definitely something still in the pitch," said Pollock. "As a batsman you never feel comfortable. It's difficult to play shots with any sort of certainty. From our perspective the situation can only get better the more runs we get."
Boucher hit 55 not out and shared an unbeaten ninth wicket stand of 56 with Andre Nel (18 not out) which tilted the balance back towards South Africa after Stuart Clark and Shane Warne had bowled Australia into a strong position.
Opening bowler Clark took four for 64 and leg-spinner Warne three for 83.
Clark admitted: "It's going to be hard work for our batters but it's not impossible."
He said there was not the same amount of sideways movement there had been on the first two days but indentations on the pitch caused by the ball made for an unpredictable bounce.
Australia are likely to be without concussed opening batsman Justin Langer for the run chase, although even if he does bat he will not be able to go in any higher than number seven because of the amount of time he has spent off the field.
Langer, hit on the head by a Makhaya Ntini bouncer Saturday, stayed at the team hotel Sunday. Physiotherapist Alex Kountouri said: "He woke up still pretty groggy.
"If he wakes up like that tomorrow he will definitely not be playing. Medically, he will not be allowed to participate unless all the signs are gone."
Another Australian casualty was swing bowler Michael Kasprowicz, who bowled only two overs in the second innings because of a sore back. Kountouri said he would be able to bat, however.
South Africa seemed to be forging a strong position when they reached 100 for two soon after lunch but Clark and Warne reduced them to 194 for eight, a precarious lead of 227, before Boucher and Nel came together.
Warne made the breakthrough when Herschelle Gibbs went down the wicket to him and was caught at mid-on for 53.
Then Warne had first innings top scorer Ashwell Prince caught at leg slip for nine, before Clark dismissed South African captain Jacques Kallis for 27 and Jacques Rudolph for a duck.
Pollock, promoted in the batting order "to give the innings a bit of impetus", made an aggressive 40 before he and Nicky Boje were out in quick succession.
Australian tail-ender Brett Lee earlier scored 22 of the 24 runs added by Australia before he was last man out for a career-best 64. Australia were all out for 270, 33 behind South Africa's first innings total.
Lee was caught at deep mid-off from the bowling of Ntini, who finished with six for 100.
Lee was involved in a controversial incident off the eighth ball of the day. With his score on 45 he edged Pollock to first slip, where Boeta Dippenaar held what television replays indicated was a legitimate catch.
Lee stood his ground and was given not out after umpire Tony Hill consulted with square leg umpire Steve Bucknor.
"It was disappointing. I thought I had a wicket in the bag," said Pollock. "Boeta was convinced he had caught it. Tony consulted with Steve, who said he was unsighted, so it was referred back to Tony and he said he heard two noises."
The decision unleashed boos from the crowd following an incident Friday when Bucknor confirmed from square leg that Australia's Matthew Hayden had held a slip catch to dismiss Jacques Rudolph, even though television replays were inconclusive.
Pollock said he would be in favour of a change in the regulations to enable the decision to be referred to the television umpire if either umpire was not sure about a catch. Referral is currently not allowed unless both umpires are unsighted.