Rachel Uchitel -- Overextended in Cover-Up

6/26/2010 4:50 AM PDT BY TMZ STAFF
Rachel Uchitel -- the pilgrim of mistresses -- wore her finest gown to a 4-hour threesome in Beverly Hills yesterday ... dropping about $5,000 on a whole new 'do, including hair extensions.  But when you've got $10 million ....

We're told Tiger Woods' #1 lady went to Norma Bouza -- of the famous Cristophe Salon -- to get locked up.

Locks are hair, right?