Hugo Hofstetter crashed into the pair, the Australian dragging the Israel Start-Up Nation rider for several metres as Ewan came to a grinding halt less than 200 metres from the finish.
Deceuninck – Quick-Step's fastman Bennett eventually crossed the line but grimaced as he rested a bloodied right hand on his thigh.
The team has confirmed their medical staff examined his hand and while he did fracture any bones, he required four stitches for the wound.
“I lost some skin and needed those stitches," Bennett said. "Because when I went into the barrier, I hit the metal part, but luckily, everything else seems pretty OK.
"In the beginning, as I was lying on the road and there was a bit of shock, as I had no idea how serious it was, but it’s a good thing nothing is broken.
"I’m quite happy it will be a short stage tomorrow and I hope things will turn around for me at some point,” the traditionally upbeat Bennett said.
Ewan confirmed on Twitter he was feeling good for the sprint until Hofstetter hitched a ride.
"Perfect job by my guys today getting me into position for the sprint! Unfortunately some guy tried to hitch a ride with 300m to go and that was my sprint over
On Instagram, Lotto-Soudal also expressed their disappointment on behalf of Ewan.
After two gruelling days working for his team mates, Bahrain-McLaren's Ivan García Cortina horsepowered his way to the win over Peter Sagan (Bora-Hansgrohe) and Andrea Pasqualon (Circus-Wanty Gobert).
"It’s amazing. It’s a race I really like so it’s a nice victory," Cortina said. "I was surprised to beat Peter Sagan. I managed to find the right place to go. I went full gas.
"I suffered in the rain like everybody else. But I really like these conditions. Hopefully, it’ll go on."
Exposure to the elements out on the 212km journey from Chalette-sur-Loing to La Châtre threatened more crosswinds, but the peloton ultimately found little interest in forcing splits, riding piano - the race finished around 40 minutes after the slowest scheduled time - for the entire stage after two gruelling days and an individual time trial ahead on Stage 4.
The standings of the main GC favourites remain largely unchanged.
LIVE coverage of Paris-Nice 2020 continues with the Stage 4 individual time trial on SBS and via SBS On Demand / our website 0.40am AEDT Thursday morning.