Lokomotiv are level on points but second due to Zenit's superior head-to-head record.
Chasing their third league title, Lokomotiv went close to scoring in the 89th minute when Uzbekistan defender Vitaliy Denisov rattled the cross bar with a rasping shot from outside the area.
The home side, who went top of the league for the first time in 86 months on Monday, finished the tense affair with 10 men after Diarra was sent off for a second bookable offence.
"Overall I think the draw was a fair result because neither team created enough clear scoring opportunities," Lokomotiv's Belarussian coach Leonid Kuchuk told reporters. "The two teams were well-organised."
The final three league matches of the year will be played on Sunday with third-placed Spartak Moscow's visit to Rostov the most intriguing one. Spartak are four points adrift of the leaders.
The 16-team league will resume on March 8.
(Writing by Angel Krasimirov, editing by Alan Baldwin)
