Wales were slow out of the blocks in all three of their tournament warm-up games last month, but recovered to claim notable Millennium Stadium victories over England and Argentina.
World champions South Africa, though, are masters at turning the screw on opponents if they establish an early lead, and Wales assistant coach McBryde knows what is required.
"It will be very hard if we do fall behind early on," he said. "That makes it hard for us to get any sort of territory.
"We didn't manage to get a good start in all our warm-up games, but we hung on and came through. We have to make sure we start the game right, to the very best of our ability."
The Wellington weather forecast for Sunday - the game kicks off at 8.30pm local time - promises wet and windy conditions, and McBryde added: "Without doubt, the weather is going to be a factor.
"But what we can't be is overly concerned with it."
Wales will be far more occupied with making their presence felt in critical areas like the set-piece and the breakdown, especially if conditions deteriorate and the game becomes a forward-dominated encounter with tactical kickers taking centre-stage.
Englishman Wayne Barnes is in charge of the contest, and McBryde said: "He is one of the best referees at communicating with the players. We are expecting a tough encounter.
"The best players are able to adapt to the way the ref calls it on the day. If we fall foul, we've only got ourselves to blame. The breakdowns will be the key in a tough game.
"He (Barnes) is very vigilant, and we are really comfortable with the way he has refereed games in the past, so I don't see that as an issue."
And one of the key individual battles promises to be a breakdown tussle between Wales captain Sam Warburton and his opposite number Heinrich Brussow,
Warburton has proved himself to be a world-class operator in that area, despite his relative lack of Test match experience, and he is crucial to Welsh victory hopes.
One of Warburton's back-row colleagues Ryan Jones, meanwhile, is fighting to avoid injury destroying his hopes of playing in the World Cup.
The former Wales captain has an ongoing calf muscle problem that ruled him out of contention for the Springboks game.
And it has emerged that back-row forward Jones is also likely to be unavailable for Wales' next two group fixtures after the Springboks against Samoa and Namibia.
Wales conclude the pool phase against Fiji, ahead of a potential quarter-final in Wellington a week later.
"Unfortunately, Ryan missed out on the last World Cup," said McBryde.
"The medical staff are telling us he could be fit, if all goes well, for the Fiji match.
"We will wait and see after the weekend where we stand injury-wise. He does have a realistic opportunity, at this stage, of taking part in the World Cup.
"He spoke to the group this morning, and he spoke very well.
"It's tough for him at the moment, but everyone is doing their best to put their arm around him and keep him going.
"He is showing true grit. All the players can take a leaf out of his book."
Wales coach Warren Gatland will need to make a decision at some stage whether or not he keeps 53 times-capped Jones with the squad or summons a replacement.
Leading candidates to take over from the 30-year-old would include Scarlets forward Josh Turnbull and former Gloucester skipper Gareth Delve, who currently plays Super Rugby with Melbourne Rebels.
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