The commissaires had to go to the photo, Peter Sagan (Bora-hansgrohe) proving once again he's always in contention for the win, nearly adding to his 11 Tour de France stage victories.
Boxed in by Sagan, Tour debutant Caleb Ewan (Lotto Soudal) hesitated when he had a micro moment of space, crossing the line for third.
Fellow Aussie Michael Matthews (Sunweb) launched his sprint a touch too early at around 300m to go and before Sagan, but hung on for sixth.
Already being hailed "super-sub" for taking over when Groenewegen couldn't, Teunissen said he was still feeling the loss of his team leader.
"Our plan was ruined when Dylan [Groenewegen] crashed," the race's first leader said. "I couldn’t clearly see if he went down but when I realised he did, I was still able to sprint. I was feeling fresh as we didn’t do much before the sprint.
"Wout [van Aert] was still with me. It’s a really strange day because our goal vanished in a second. I hope Dylan smiles as I replaced him for the win. It’ll take me a few days to understand what’s happening to me, especially with the yellow jersey, but we have another big goal with the team tomorrow."
[tdf widget="stagewinners" stage="1"]
Around 17 kilometress before Groenewegen's bingle, pre-race favourite Jakob Fuglsang was also felled by a crash, skulking back to the peloton under the escort of his Astana team, blood pouring from a gash above his right eye and knee.
Earlier in the stage, the race got underway with an aggressive move from Greg van Avermaet, jumping into the early breakaway. With one job on his mind - to lead the race over the iconic Muur van Geraardsbergen - Greg van Avermaet doggedly initiated the day's break with the drop of the start flag drawing Natnael Berhane (Cofidis), Mads Würtz Schmidt (Katusha) and Xandro Meurisse (Wanty-Groupe Gobert). After collecting enough points over the first two climbs, the proud Belgian re-joined the peloton, his national duty rewarded with the polka dot jersey in Brussels.
Avermaet's three breakaway companions were caught with 70kms to go, leaving the sprinters' teams to position for the final sprint.
Stéphane Rossetto (Cofidis) tried a move with 40 kilometres remaining in the race, but although he was given a bit of leeway by the peloton, he was easily recaptured in the run to the line.
Australia's top sprinter Caleb Ewan didn't go away empty handed after his first stage of the Tour de France, making a trip to the podium as the owner of the white best young rider jersey.
[tdf widget="tourleaders" stage="1"]