The Cambusdoon side, who have defied the odds all season, went in to their final match of the season on the back of their only defeat of the campaign. Last week's heavy reverse to Clydesdale meant they still needed four points to deny the Titwood outfit the chance to come from behind to claim the honours.
In the circumstances and with so much at stake, Ayr were entitled to show signs of nerves and these were in evidence in the early stage of their innings as the steady fall of wickets saw them precariously placed on 172-6 with just five overs remaining.
However, some lusty late hitting from the tail-enders hoisted the tally to an impressive 246. The tension was still in evidence when Dumfries reached the half-way stage of their innings with just two wickets down but Ayr's bowlers ultimately took a stranglehold on proceedings.
The win completed the club's first Union title since 1996, an era dominated by such luminaries as former Scotland opening batsman Bruce Patterson, the equally prolific Albert Simpson and ever-reliable medium-pace bowlers in the shape of Andy Baird and Mark Renny.
Now, under the leadership of the inspirational Andi McElnea, a new generation have made their mark on the Scottish game and a delighted Ayr captain said: "We're absolutely thrilled that our hard work has paid off. This time last year we were at Stirling in a game we needed to win to stay in the top division and, to be honest, our target at the start of the season was simply to stay in this division.
"But as the season has gone on we have been able to revise our aims upwards and it's a great feeling to get the job done."
While Zimbabwean professional Sikander Raza played his part in the success and will finish the season as the Union's top run scorer, despite having departed on international duty six weeks ago, fittingly it was Ayr's young brigade who largely carved out yesterday's clinching victory.
Shujaa Khan was their top scorer with a patient innings of 49 when the pressure was on, while McElnea's young brother Scott was the most impressive of the late hitters with a blistering 39. The younger McElnea, a former Scotland U19 World Cup player, was also Ayr's most successful bowler, claiming 3-25, while Steve Liburd, the Leeward Islander who replaced Raza, claimed 3-52 as Dumfries were dismissed for 185 despite solid resistance from Scott Beveridge who made 47.
"The young players will take tremendous confidence from what they've achieved this season and hopefully we can build on this success next season," added McElnea.
Ayr will defend their crown in an expanded 10-team league next season, First Division champions Ferguslie having yesterday been joined in the top flight by Paisley rivals Kelburne who clinched their place with victory over Stirling.
Meanwhile, RH Corstorphine won promotion to the CS Eastern Premier Division after a play-off win against Strathmore & Perthshire Union champions Meigle. In a low-scoring encounter at Scroggie Park, Falkland, the Edinburgh side looked to be struggling after being dismissed for just 127.However, a superb display in the field saw them hit back to skittle Meigle for just 57.