It was barely 12 hours since Kipyegon successfully appealed to overturn her disqualification from the 5,000m after a mid-race altercation with Tsegay in which both narrowly missed crashing onto the track.
Kipyegon, who broke her own world record in the 1,500m a month ago, seemed to be conserving energy at the end of her heat, letting the US’ Nikki Hiltz pass her in the final straight once she was confident she was in the top six who would move on to semifinals.
“To tell the truth I am a bit tired but I feel fresh,” defending Olympic champion Kipyegon said afterward. “This is another race, another distance. I’m really good, mentally.”
Welteji, who won silver at last year’s world championships, won that heat in 3:59.73s with the UK’s Georgia Bell right behind her and Hiltz finishing third.
The first heat was the fastest, with Tsegay taking the lead from the halfway point and finishing in 3:58.84s.
Laura Muir, who won silver in Tokyo, made a push to take second place, and stretched ahead with 100m to go but ultimately finished seven-hundredths of a second behind Tsegay.
Kenya’s Nelly Chepchirchir won her heat, maintaining her composure in a scrappy race that saw early frontrunners like Uganda’s Winnie Nanyondo and Ethiopia’s Birke Haylom running out of steam to end 10th and 11th.
Chepchirchir was in the lead by the end of the first lap with Nanyondo right behind her, but Haylom made a break for it halfway through the race, with Australia’s Jessica Hull also picking up the pace to stay on her shoulder.
It was 21-year-old Chepchirchir, though, who found a higher gear in the last lap and powered ahead, daring Hull to follow her. The Australian finished in 4:02.70s, just behind Chepchirchir.
“You’ve got to take it one run at a time. People ran today like it’s the final. So, one at a time,” Hull said.
The first six in each heat advanced to the semifinal on Thursday at 7.35pm local time, with all the others going to a repechage round set for Wednesday at 12.45pm local time.
Medallists will be decided in the final at 8.15pm on Saturday.