Benoot was the only rider from the remains of the day's break who could follow the South African's surge 12 kilometres from the finish on the Cote de Saint-Just.
As expected, Mitchelton-Scott's Mr Versatile possessed the necessary kick to win it on the line and grab his first individual Tour de France stage victory, after tasting success with the team in 2013 in the TTT.
“Pretty much, for me, from a Tour de France perspective, a stage win was something really missing," Impey said.
"I made quite a few breakaways in the past few years and finally, today, I got the win on Bastille Day. It’s fantastic!
"It’s a dream come true. It’s so difficult to win at this level.
"I kind of marked this stage. I was lucky to find the right move. We all worked well together. I’m glad the legs were there at the end to beat Tiesj Benoot. I haven’t been emotional like that for a long time. I think the last South African to win a Tour de France stage was Robert Hunter in 2007… it’s a magic victory.”
Race leader Julian Alaphilippe and the GC favourites took the stage easy finishing just over 16 minutes behind Impey and Benoot in a reduced peloton. Just Romain Bardet tried something on the final climb as they headed to his hometown Brioude. But Richie Porte (Trek-Segafredo) and George Bennett (Jumbo-Visma) comfortably and confidently quelled the Frenchman's move, drawing a response from a Michal Kwiatkowski-led Ineos and the rest of the bunch. But most importantly, Porte safely finished the ninth stage of the Tour, the first time he has managed the feat since 2016.
Impey and Benoot jumped away with 12 other riders in the opening kilometres, a break featuring notable names like Simon Clarke (EF Education First) Lukas Pöstlberger (Bora-Hansgrohe), Oliver Naesen (AG2R-La Mondiale), Tony Martin (Jumbo Visma), Jasper Stuyven (Trek-Segafredo) and Nicolas Roche (Sunweb). They built a three minute advantage by the 25th kilometre with Marc Soler (Movistar) and Rui Costa (UAE) in hot pursuit, but at different points back down the road.
While Soler made it across to the leaders one kilometre from the top Mur d'Aurec, Costa lived to fight another day, dropping back and waiting for the peloton.
Aussie Clarke was the first to attack, 62 kilometres from the finish but he was quickly reeled in. Ivan Garcia Cortina (Bahrain Merida) tried 20 kilometres later, Pöstlberger reacting with an attack of his own on a non-categorised bump before the Cote de Saint-Just. This move split the leading bunch into two with seven chasers including Impey, Benoot and Roche the closest to Pöstlberger. But the Austrian found the going tough on the final climb as Impey soon rocketed past with Benoot on his wheel.
The 170km stage from Saint-Etienne was marred by a nasty crash within the first 10 kilometres which saw yesterday's breakaway artist, Alessandro De Marchi deaprt the race, the CCC rider breaking a collarbone and fracturing his ribs in the fall.