During the week Thistle had made it two wins from two in the league as they thumped their derby rivals St Monans Swallows 5-3 away from home.
Thistle then travelled to Dunfermline a few days later to face bogey team Rosebank a side who they had failed to beat in the previous eight encounters.
Thistle should have opened the scoring with only three minutes on the clock when Barnes set Harrow through on goal but, with just the keeper to beat, the striker’s tame effort was easily blocked by McKinnon.
Thistle were dominant in the opening 20 minutes, but the worrying sign was the inability to convert chances as Harrow, Barnes, Shepherd and Ireland all passed up good chances.
The second half started with Rosebank beginning to take the match to Thistle and with 55 minutes gone they opened the scoring with only their second effort on target when Stephens was allowed too much space from Moir to head home an Ellis free kick.
Once taking the lead the hosts seemed happy to sit in and absorb the pressure as Thistle looked to find the way through what was proving a resilient defence.
It looked as though Thistle were going to fail to score in a match for the first time since a 4-0 defeat to Auchtermuchty Bellvue in March 2015.
But in the final minute of the game Henderson sent a long ball up the park and Harrow reacted fasted to take advantage of hesitancy in the home defence to prod the ball home and grab a share of the spoils and maintain Thistle’s unbeaten start to the season.
Mn of the match – Mark Gorgon
Thistle – Henderson, Ireland, Gorgon (Capt), Thomson (Carson 66), Gough (Love 80), Shepherd, Foulkes (McShane 66), Moir (McArthur 56), Jukes, Barnes, Harrow.
Sub – Anderson.
Tomorrow (Saturday) Thistle play host to Premier League side Kirkcaldy.