Toronto (2-10-4) and Philadelphia (4-9-2) have the worst records in MLS. But both teams have shown signs of life since changes were made on the sidelines, with Paul Mariner taking over in Toronto and John Hackworth taking charge in Philadelphia.
TFC is 1-1-4 under Mariner while Philadelphia is 2-2 under Hackworth in league play.
The Union is coming off a 2-1 win in Los Angeles, thanks to a stoppage time goal by Michael Farfan.
Koevermans scored for the fifth time in as many games in a 1-1 tie in Dallas on Wednesday before limping off in the 87th minute after trying to keep a ball in play at the Dallas goal-line. Dunfield had exited minutes earlier after taking a nasty blow around the eye.
Koevermans' goal showed the artistry of a pure goal-scorer. After Eric Avila drove the ball towards goal, the big Dutchman stuck out his right leg — as if doing a little dance — and flicked the ball in.
It was like a hockey forward redirecting a puck in front of goal.
"Just natural goal-scoring ability. You've either got it or you've not got it," said Mariner, who had it during his playing days in England.
Mariner, who calls Koevermans' current goal-scoring run staggering and remarkable, was even happier at the number of phases that led to the goal.
After Dallas midfielder James Marcelin, fending off Koevermans' presence, headed a Milos Kocic goal kick back towards the Toronto end, TFC captain Torsten Frings chested the ball down to Jeremy Hall. The right fullback eluded a Dallas player and floated a ball into the Dallas penalty box.
Defender Matt Hedges cleared it but Dunfield intercepted and sent a dangerous cross across goal. Koevermans, between two defenders, missed it but Marcelin's attempt to chest the ball down only sent it to Toronto's Reggie Lambe at the edge of the box.
The Bermudian international stuck out his left leg and poked the ball towards goal. Toronto forward Ryan Johnson couldn't get to it but defender Matt Hedges' awkward clearance went to the side of the goal, where Koevermans and Colombia defender Hernan Pertuz collided at the far post.
Pertuz's clearance went only as far as Avila in the corner of the box. He sent in a left-footed cross and Koevermans — with Pertuz clutching his head on the ground — worked his magic.
The whole play took just 40 seconds and was a thing of beauty for Mariner, who relished the number of touches that led to the score.
"That's an important aspect," he said. "Because I think maybe a few weeks ago, we wouldn't be getting those phases but now we are."
Koevermans, who joined the team mid-season last year along with fellow designated player Frings, has scored a remarkable 17 goals in 18 career MLS starts.
Considering injuries and a slow start this season, his numbers are even more eye-popping.
On Wednesday, he felt a tweak in his right knee after stretching for the ball.
"I spoke to him in the morning and he said he thinks he's going to be OK," said Mariner.
Should Koevermans be unable to go Sunday, Mariner can look to Luis Silva, Avila, Nick Soolsma or Lambe up top with Ryan Johnson.
Sunday marks Toronto's seventh game since resuming play June 16 after the international break.
It's the sixth game for the Union over the same stretch and it had U.S. Open and friendly games earlier in June.
Philadelphia also faces three games in six nights, against Toronto, Sporting KC and Montreal.