Ulster took the lead early in the match but were held to a 33-33 draw by Glasgow Warriors.
The hosts, seeking their first win in Derry since last season, started strongly with Bryn Ward scoring on a short penalty kick in the fourth minute.
Jack Murphy converted to put Ulster ahead 19-14 at the interval.
Glasgow responded clinically within nine minutes when Josh McKay scored a try following a flowing move.
Kyle Rowe then crossed after a pass from centre Stafford McDowall, which resulted in three Ulster players being sin-binned.
Horne converted again to give Glasgow a two-point lead before the second half began.
Ulster sought revenge when McIlroy made an offload that allowed Richie Murphy to score a try in the final play of the first half.
However, indiscipline cost the hosts as Ben Carson was sent to the sin bin for a high tackle on McDowall.
McIlroy was subsequently carded for a deliberate knock-down, leaving Ulster with 13 players on the field.
Despite having Carson back on the pitch, Rowe raced clear to extend Glasgow's advantage after soft defending from Ulster.
Jacob Stockdale, set to win his 150th cap, was forced out of the starting team during warm-up but did not impact the visitors' early performance.
Rory Darge and Talakai were sin-binned inside the final ten minutes due to repeated infringements.
Ulster camped on the Glasgow line while Augustus crashed over for a try that levelled the score at 33-33.
Nathan Doak converted to keep the match deadlocked in front of the Belfast crowd.
The decision regarding George Horne's late penalty was reversed after he threw the ball at Ulster hooker Tom Stewart during the incident.
Glasgow had previously lost their opener against Edinburgh but started this fixture as the better side.
There was a final twist when Horne won a penalty but retaliated by throwing the ball at Tom Stewart, leading to the decision being overturned.
The match ended without a winner after both sides played out a thrilling contest in the United Rugby Championship.