Mont Ventoux is often described as a mountain with a personality and a particularly malevolent one at that, so the bizarre Bastille Day finish at Chalet Reynard seemed somehow in character for a mountain which has ended dreams, careers and lives when the Tour de France has scaled its heights.

The sight of the yellow jersey, Chris Froome, running up Mont Ventoux without his bike was surreal, on a par with the episode at Gap in 2003 when Lance Armstrong was forced to take a short cut across a field to avoid a crash and ran back on to the road with his bike on his shoulder, cyclocross style.

The chaos on the road was followed by confusion among race officials over the yellow jersey and it all stemmed from the latest in a long series of incidents in which spectators and race vehicles have affected the race, sometimes to far more dangerous effect – the gendarme wielding a camera who brought down the bunch sprint at Armentières in 1994 and the television car that took out Johnny Hoogerland and Juan-Antonio Flecha in 2011, to mention only two.

The background issues are complex: a sport held on open roads that is uniquely vulnerable to outside interference, where over succeeding years more and more fans have taken to running as close to the riders as they can, ignoring constant pleas to keep clear, as recently as last Saturday from Froome himself. For years there have been complaints the Tour is getting too big for its own good – and that of the men who risk their lives to race it – and this will merely accentuate the debate.

Similarly, the scale of the caravan of motorbikes and cars is a continuing problem, which has caused other more serious accidents in other events this year; but the specific issue on the Ventoux was that the motorbikes had nowhere to go because of the weight of fans pressing on to the road. Similar scenes are witnessed each year, if not quite as extreme as this, and in that sense this was an accident waiting to happen.

“There were so many motorbikes in the way, it wasn’t safe,” said the Frenchman Romain Bardet. “You had to brake when you were attacking. We need to have a long conversation about security here. It was unacceptable, what happened today.”

The bizarre sequence of events obscured the sporting picture. In the context of the Tour’s three weeks this was not the conclusive result it might have proved had the finish been held adjacent to the observatory six kilometres higher up the mountain. The stage ended at the treeline to spare the riders being exposed to the dangerously strong winds on the bare upper slopes. Froome attacked in the final kilometres yet was unable to show the same strength he had displayed here in 2013, but all his rivals looked little better.

When the race leader, Richie Porte and Bauke Mollema collided with the television motorbike, the trio had pulled clear of the remains of the main group, but not decisively so. Mollema finished 19 seconds ahead of Nairo Quintana, Adam Yates and company, so Froome was credited with his time, as was the Australian, meaning the overall standings barely changed before Friday's time-trial stage westwards into the Ardèche. The only major casualty was the Irishman Daniel Martin, who slipped off the pace seven kilometres from the finish and dropped from third to ninth overall.

A few minutes ahead of Froome and company, the stage win was contested by the remains of a 13-rider escape which included a handful of Frenchmen looking for a prestigious win on the Fête Nationale, but the home men froze and the surreal finish became a Belgian story, as the French term a bizarre event in which their neighbours are involved.

The final two survivors were Thomas De Gendt of the Lotto team and Serge Pauwels from Mark Cavendish’s Dimension Data, and it was De Gendt who showed the greater strength in the final metres.

To rub salt in wounded national pride, he relieved Thibaut Pinot of the King of the Mountains jersey.

As predicted, the wind played its part well before the foot of the mountain was reached. The Etixx team did much of the damage, pulling a 40-rider group two minutes clear of the rest of the peloton, with the aim of eliminating Fabio Aru of Italy and Warren Barguil of France, two possible rivals to Martin for a high overall placing.

The Italian struggled with mechanical issues all day but was finally saved when a crash involving Simon Gerrans of Orica-Bike Exchange and Team Sky’s Ian Stannard caused the front group to slow down at Froome’s prompting.

As on Wednesday, the constant effort and cumulative fatigue played its part in the final showdown and, ironically in view of earlier events, it was Martin who lost time on the mountain. The Ventoux stage was the first of two consecutive days that will help to define whether Froome is likely to win his third Tour, and who, if anyone, may challenge him; the second is Friday’s 37.5km time trial finishing at La Caverne du Pont d’Arc.

The course includes two hills and a lengthy stretch along a plateau, where the north wind – forecast to blow at 30kph – could make this even harder than expected.

Froome said he expected to gauge his effort on the Ventoux so he would have some strength left in his legs for stage 13 but he would never have expected them to have to do quite what he asked of them in the final kilometre of stage 12.

(Guardian service)