The 7,461 crowd saw Ulster win 29-21 to maintain their winning run and the landmark five millionth customer for the Magners League enjoyed another trademark close encounter.
Andy Irvine, the newly-appointed Celtic Rugby Chairman, said: "It is fantastic to think we have now broken through the five million mark in terms of fans through the gate and the signs are that our gates are rising across the board this season.
"The Scarlets have opened with two 6,000-plus crowds and Glasgow have continued their upward trend after showing a 26% increase on their gates last season.
"We have come a long way since the first Celtic League game was played at the Brewery Field, Bridgend, between Bridgend and Pontypridd on August 17, 2001. Ulster also played on that night, beating Swansea 30-13 at Ravenhill in front of a 6,000 crowd.
"There have been many changes to the format of our competitions since then, but the introduction last season of the play-offs and grand final to determine the Magners League champions was hugely significant and successful.
"With the introduction of the two Italian teams we now boast more than 280 international players playing within our 12 teams and the quality of the competition is now a match for any league in the world.
"Having just reached the five million landmark with our fans, everyone is now looking forward to a record breaking gate at the Aviva Stadium on Saturday, October 2, when Leinster host Munster in what is likely to be the biggest club game in Europe that weekend.
"With more than 40,000 tickets already sold for that fixture, a full house of 50,000 is being anticipated. It is onwards and upwards for the Magners League."