San Francisco commuters who use the Muni underground likely encountered some trouble Monday if they were trying to get home after 6 p.m., and it's because of what SFMTA officials said was a "determined and elusive" dog running in the downtown tunnel.

How did a dog get into the Muni tunnel Monday? It's anyone's guess, but the dog got away from its human around West Portal, sometime around 6 p.m., and as the Chronicle reports, the SFMTA began ordering Muni trains to be slowed and began warning commuters of delays.

SFMTA's first tweet about the incident came at 6:08 p.m.

"It’s been over an hour and you still haven’t gotten the dog out of the tunnel?" replied one X user about an hour later.

"Not yet. The dog is very determined and elusive," the SFMTA replied at 7:15 p.m.

Around that time, the dog was spotted in the trackway between Church and Van Ness stations.

Meanwhile, bus shuttles were being used to replace train service.

Animal Care & Control officers were brought in to assist, but to no avail.

And it turns out the pooch had energy to burn, and s/he ran the entire length of the tunnel in the course of two hours, making a beeline for downtown, running from West Portal to Embarcadero Station.

By 8:21 p.m., the SFMTA tweeted that they had been unsuccessful in catching the dog, and s/he was last seen running out of the tunnel at Ferry Portal — the place where trains come above aground on the Embarcadero, near the Ferry Building.

Inbound M and K train service from West Portal, and outbound service from Embarcadero, resumed around 7:40 p.m., after the dog was seen in the tunnel out past Embarcadero.

The bus shuttle service along Market Street, between Embarcadero and West Portal, continued through 10 p.m. to make up for delays in the system.

There's no word on whether anyone has claimed the dog, or if s/he was located anytime later, chilling in SoMa or down by the ballpark.

Previously: Young Pitbull Pup Found Wandering on Bay Bridge