The 22-year-old Aberdonian, who won the British title last month, set the tone with a strong opening leg as the home team clocked 3:24.74, well behind the imperious Americans, who are clear gold medal favourites, but equally comfortably in the second automatic qualifying spot.
Clark handed on to Laviai Nielsen before Perri Shakes-Drayton and Emily Diamond brought the baton home well clear of third-place Botswana.
GB captain Eilidh Doyle could come in for tonight’s final, where it looks like a medal could be there for the taking. Jamaica won the second semi-final just over a second quicker than the British team.
“I quite like doing it [first leg],” said Clark after the race. “I’ve not done it overly often but I was quite confident coming into it.
“We knew the Americans were going to be out strong so it was about sticking as close to them as possible and I think it went well.”
Anchor runner Diamond added: “The first round is about getting the job done and qualifying for the final, but I think we all ran really well. The crowd just backed us the whole way and it was like a Mexican wave of cheer going all the way round.
“It was phenomenal running there this morning and hopefully we can come back tomorrow and get the job done. We still have two girls in the team who haven’t run today so we have great strength and depth.
“I think whatever team runs tomorrow they will have a great shout of bringing back one of the medals. It should be good fun, I can’t wait.”
The men’s 4x400m relay team also made the final but in a much more turbulent manner.
Firstly they had to rely on a fastest losers’ spot after finishing fourth in their heat and then some apparent team friction emerged as anchor runner Martyn Rooney seemed to hint that British No.1 Matthew Hudson-Smith had walked out on the squad.
Hudson-Smith, who failed to progress from the individual semi-finals here, was the man whose error led to GB being disqualified at last summer’s Rio Olympics when part of his foot strayed out of the takeover zone.
“As far as I’m aware, Matt has taken himself out of the team,” said Rooney. “He has got his own issues to sort out. It’s a massive shame, he’s a super talent… but he has got to get his head right.”
British Athletics, however, insisted that Hudson-Smith was still part of the squad and could come in for tonight’s final, which saw the Americans qualify fastest. The GB team were edged into fourth behind Trinidad & Tobago and Belgium.
Australia’s Sally Pearson reclaimed the world women’s 100m hurdles title she last held in 2011. The 2012 Olympic champion, now 30, won in 12.59sec from Dawn Harper Nelson of the USA and Germany’s Pamela Dutkiewicz.
Britain’s Katarina Johnson-Thompson and Morgan Lake finished fifth and sixth respectively in the women’s high jump.
They both failed to clear 1.97 metres. The gold went to “neutral” Russian Maria Lasitskene who cleared 2.03m.