Lindsey Vonn -- TIGER DIDN'T LIE ... About Missing Tooth Story

Another bizarre twist in the Tiger Woods missing tooth mystery -- his GF Lindsey Vonn is backing his "camera smacked me in the mouth" story ... despite eye witnesses who claim it's all BS.

Vonn just went to Facebook to back up Tiger's story about why he was pictured without a front tooth at the World Cup skiing event in Italy this weekend -- saying:

"I feel terrible that his tooth got knocked out though. When he was in the finish area a camera man accidentally knocked into him and took out his front tooth. He was still in great spirits though and didn’t complain once or ask for any special assistance or security."

Problem is ... event officials have gone on the record and said no such accident ever occurred and if it had, there would have been witnesses or video of the incident.

One official told TMZ Sports that Tiger never even showed signs of pain ... signs that you'd expect someone to have after losing a tooth.

But Lindsey came up with an explanation when talking to USA Today -- saying, "This pain is really nothing when he has had as many injuries as he's had. It's not a big deal. He was in good spirits."