And after adding a fifth following the restart Hobbs went over midway through the second half to secure the win, despite a late Dave Moore try in return.
Connacht had not won away since the opening day but started this game on the front foot, getting on the scoreboard after just three minutes as Niall O'Connor kicked a penalty.
Just two minutes later however and the scores were level as Blair replied with a three-pointer of his own, the full-back then converting his second on eight minutes to put the hosts in front.
And that is how it stayed until the 16th minute as following a great lineout by Mike McCarthy Connacht spread the ball the width of the pitch for O'Halloran to touch down in the corner.
O'Connor made no mistake with his touchline conversion and the visitors had a 10-6 lead.
But that was as good as it got for Connacht in the first-half as on the half hour Blair kicked another penalty, before adding a fourth on 36 minutes for a 12-10 half-time lead.
Just five minutes into the second half O'Connor had the chance for Connacht to retake the lead but his three-point effort fell just short of the posts.
And he was made to pay for it six minutes later as Blair kicked his fifth penalty of the game to open up a five point lead.
This turned into an unassailable 12 points just after the hour mark as prop Hobbs touched down under the posts and Blair added the simple extras for a 22-10 lead.
Despite this Connacht still looked dangerous on the break but just couldn't find the finishing touches until it was too late.
With the final whistle looming a great cross-field kick from full-back Gavin Duffy found O'Halloran and he helped Moore across the whitewash for a deserved second try.
But it was all too little too late and replacement Matthew Jarvis' missed conversion summed the game up for Connacht as Cardiff picked up the win.
|Cardiff Blues Score Card|
|Connacht Rugby Score Card|