Koonibba saw off the challenge of Thevenard in an opening round Far West Football League thriller on Saturday, emerging victorious by five points.
The two evenly-matched teams traded the lead in the Anzac medal game, only for the Roosters to come away with a 14-12 (96) to 14-7 (91) result.
Tjerayh Ware led the way for the Roosters with three goals, while Dom Denton kicked five for Thevenard and was helped by four apiece from Josh Cummings and Jarrad Trowbridge.
His five-goal haul saw Denton named the Anzac Day medal winner, while Josh Wilkins was another to impress for Thevenard.
Koonibba's best included Waylon Johncock and Wesley Tschuna.
It was Koonibba - last season's beaten grand finalists - who had the better of the opening quarter as they raced away to a three-goal lead by the first change.
Yet the Magpies roared back into the contest in the second term with a seven-goal display which turned the deficit into a two-point advantage at half-time.
That set the stage for a fascinating second half.
Koonibba wrestled back the lead by eight points at three-quarter time after kicking three goals to two.
It proved just as close in the fourth term as both teams added three majors, with Koonibba holding on to start 2019 on the front foot.
Western United opened its premiership defence with a 159-point thrashing of the Blues.
The Blues had no answer for a second-quarter onslaught which led to a 25-24 (174) to 2-3 (15) result.
Just 10 points separated the sides at quarter-time as the Tigers could only manage one goal from seven scoring shots, but they found their rhythm once play resumed.
Western United raced away with nine goals and seven behinds in an awesome display, while also restricting the Blues to a lone major.
There was no let-up after half-time as Westies added another four goals to the Blues' one which extended the margin to 88 points by the final break.
As the Blues ran out of steam, the visitors were just getting going.
They added to the carnage with 11 goals in the final quarter while also restricting the Blues to a single behind.
Last season's leading scorer Jarden Stoetzer showed there was no rust with six goals to start 2019, as Tom Woods booted five.
Garrett Bowden and Dylan Cook got the two goals for the Blues.
Jake Warmington and Jesse Chandler impressed for Western United, while John Dunn and Brendan Kloeden did their best for the Blues.
In the B grade, Koonibba eased to a 105-point rout against Thevenard.
The Magpies failed to kick a goal and did not get on the scoresheet until the final term as it ended 15-17 (107) to 0-2 (2).
Vaughan Day grabbed three goals for the Roosters.
Koonibba kicked nine goals to half-time and added another six in the resulting two quarters for a comfortable opening day triumph.
Western United got the better of the Blues by 44 points thanks to a dominant final quarter.
A close contest for three quarters, the Tigers eventually picked up the points with a 9-7 (61) to 2-5 (17) victory.
Just 13 points separated the teams at half-time and Westies pushed the margin out to 19 by the final break.
They then kicked four goals to one behind to grab the victory.
Tigers player Brent Dunn, four goals, was the only player to kick multiple goals.