Dakota Johnson took to NBC's iconic Studio 8H for her 'SNL' hosting duties -- but the "Verity" star wasn't alone for her monologue ... because Taylor Swift crashed the show.

All eyes were on Dakota when she strutted on stage in a red latex dress while delivering some not-so-subtle jabs at the public breakups she's had -- with Role Model and Chris Martin -- since her last time hosting "Saturday Night Live."

Dakota told the audience that she's been able to get through the breakups because of her amazing friends -- and Taylor is apparently so amazing that she came to support her "Patient Zero" costar during her big moment.

During the monologue ... Dakota called TS "her therapist" to which Tay responded that she was not her therapist -- the actress just shows up at her house once a week and has to be driven home by the pop star's security.

As we previously told you -- Dakota starred alongside Colin Farrell in Taylor's newest music video "Patient Zero" ... taking their friendship, or rather therapist-client-relationship, to a whole new level.

No word yet on if Taylor will be popping into any more sketches ... stay tuned.