It came in an eventful finale to the 181 kilometres trek from Montbrison in which Michal Kwiatkowski, the leader at the beginning of the stage, crashed hard with 1.3km remaining. 

The Pole recovered to ride by himself to the line and was awarded the same time as all other riders due to the crash happening in the closing stages.

Impey, however, leapfrogged the Team Sky rider in the overall standings due to a time bonus he received for finishing third on the stage.

The South African, riding for Mitchelton-Scott, produced a strong late burst to cross third.

He was beaten only by Bora-Hansgrohe's Ackermann and Norway's Dimension Data rider Edvald Boasson Hagen, who finished second.

The result marked Ackermann's second professional victory after a stage win at the Tour of Romandie earlier this season.

All the leading riders were awarded the same time of 4 hours 19min 57sec.

Impey now leads Kwiatkowski by two seconds in the overall standings.

Gianni Moscon, another Team Sky rider from Italy, is three seconds further back in third.

Tomorrow will consist of a 35km team time trial from Pont-de-Vaux to Louhans-Châteaurenaud.

It will be followed by four tough mountain stages, where the overall contenders are likely to emerge.

The race is part of the International Cycling Union World Tour.