Spencer Pratt's Los Angeles mayoral dream won't come true this year ... because he finished third in the primary election and won't advance to the runoff.

Mayor Karen Bass and City Councilwoman Nithya Raman won more of the vote than Pratt ... meaning the two will go head to head in the general election on November 3.

Now that 92.5% of the expected votes have been counted, Bass remains in the lead with 34.3% while Raman earned 28.5% of the vote compared to Pratt sitting at 25.8% ... according NBC.

Pratt's campaign generated a ton of buzz ... with politicians in the upper echelons of government -- from President Donald Trump to Senator Ted Cruz and even AOC -- weighing in on Pratt's run for the mayor's mansion.

Earlier today, POTUS unloaded on Truth Social after new vote totals showed Pratt slipping out of runoff-advancing position in the Los Angeles mayoral race. Trump called the result impossible, blasted the city's election process and declared a "rigged" election.

Pratt ran on a platform of cleaning up the city streets and rooting out corruption in the government. He lobbed multiple attacks on Bass since announcing his campaign in January ... but, it seems he didn't get through to as many prospective voters as he may have thought.

Pratt was very confident ... telling us back in February he was going to crush Bass.

Sorry, Spencer -- maybe 2030 will be your year?