Umtiti was on hand seven minutes from time to score with a deflected shot, restoring parity after Edinson Cavani's first-half header to add to the home side's indifferent form.
Despite their unbeaten opening to the campaign, a run of three consecutive draws in all competitions is likely to lead to further speculation surrounding Blanc's position at the club, with fans growing increasingly frustrated at a perceived sluggish start to their title defence and in Europe.
They were given a good contest by visiting Lyon, who threatened to make a breakthrough before Umtiti's strike before half time when Arnold Mvuemba's free-kick cannoned back off the woodwork.
The hosts thought they had earned a win at the death when Marco Verratti headed home late on, but the Italian's effort was ruled out for an earlier foul.
Despite Blanc facing criticism in the build-up to this match, he would have been pleased with his side's early efforts at the Parc des Princes.
The hosts had an appeal for a penalty turned down after 12 minutes, when Blaise Matuidi's cross appeared to come off the arm of Bakary Kone, before Yohan Cabaye latched onto Zlatan Ibrahimovic's flick-on inside the box and fired wide.
Lyon, who made just one change from their surprise win over Monaco last week, struggled to get out of their own half and found themselves behind on 21 minutes.
A teasing cross from Lucas Digne on the left found Cavani at the far post, who diverted an expert header beyond the reach of goalkeeper Anthony Lopes.
Alexandre Lacazette nearly responded for the visitors on 25 minutes, but drilled harmlessly wide, before Mvuemba rattled the crossbar five minutes later with a curling free-kick from just outside the box.
Cavani spurned a gilt-edged opportunity to double his tally eight minutes before the break, firing high and wide after an onrushing Lopes fluffed his punch during an aerial collision with Ibrahimovic.
Matuidi diverted an angled volley wide nine minutes into the second half, but the hosts seemed happy to simply keep possession as the period progressed, although the home faithful will have been pleased to see the return of midfielder Thiago Motta, who came off the bench on 65 minutes to a predictably warm ovation.
And he nearly helped to add a second within five minutes of his return, dinking in a lovely ball for Cavani, whose header across goal was nodded towards his own net by Umtiti, forcing an impressive save from Lopes.
Umtiti recovered from the uncertainty to strike the crucial blow with six minutes left. PSG totally failed to clear a corner and the France Under-21 defender's scuffed effort deflected off Serge Aurier and past a helpless Salvatore Sirigu.
Corentin Tolisso wasted a golden opportunity to snatch a win for Lyon and Verratti found the net, but Lucas Moura had blatantly impeded Lopes.
The final whistle was greeted by jeers from the crowd and Blanc now requires a strong response from his side when they visit Caen in midweek.
