This week’s Atlanta Symphony Orchestra performance of Beethoven’s Third Symphony was supposed to be one of the last times Donald Runnicles would direct the ASO as its principal guest conductor, a position he’s held for just over a decade.

But after months of negotiations, the orchestra and its audiences will see Runnicles at the conductor’s podium a little bit longer. Thursday, the ASO will formally announce that Runnicles’ contract, which was to have ended at the conclusion of this season, has been extended another two years through the 2013-2014 season.

For one of the city’s cornerstone artistic organizations, the retention of Runnicles is a major achievement.

“After 10 years, in some ways I feel as though we’ve just gotten started,” Runnicles said in an exclusive interview with The Atlanta Journal-Constitution. “At this stage of my career, my only ambition is to imbue my incumbent relationships with more depth.”

Much in demand internationally, the Scottish conductor is also the general music director of the Deutsche Oper Berlin, the chief conductor of the BBC Scottish Symphony Orchestra and the music director of the Grand Teton Music Festival. He and his family call Berlin home, but under this new contract he’ll spend three weeks a year working with the ASO, perhaps four, if his schedule allows.

“The thought of him leaving is something I’ve always been in denial  about,” said Robert Spano, ASO music director. “We’ve been in this since the beginning.”

Just minutes before Runnicles was to begin Tuesday afternoon rehearsals for this week’s performance, ASO President Stanley Romanstein addressed the orchestra and formally revealed the extension of the contract. Orchestra members burst into enthusiastic applause, stomping their feet for emphasis.

“Keeping Donald was our highest priority for the artistic year,” said Romanstein. “He is in such demand that finding available weeks on his calendar was the most difficult part of this. But Donald said to his managers, ‘You must find the weeks for me to be in Atlanta.’ He has an affection for Atlanta audiences and for this orchestra.”

Apart from “Eroica” this week, Runnicles will direct the orchestra and chorus next week in a performance of Mahler’s masterwork Second Symphony “Resurrection.”

During Runnicles’ tenure he was able to bring the ASO chorus to Berlin in 2009 and lead it in a performance of Brahms’ “A German Requiem,” with the Berlin Philharmonic. It was the third time he’d taken the chorus to Berlin.

In the coming years, Runnicles said, he’d like to revisit some of the work he has done with the orchestra, as well as explore work perhaps unfamiliar to Atlanta audiences.

“Usually it’s, ‘We like what we know,’” Runnicles said. “I hope this long journey helps audience members enjoy the adventure of coming to a piece they’ve never experienced before.”

It’s the 10-year relationship between Runnicles and Spano that will likely make that happen. Spano was in Berlin in December and heard Runnicles’ direct Strauss’ “Don Quixote.” At that point he knew Runnicles would likely be staying with the ASO and the mood was “celebratory,” Spano said. Their relationship through the ASO is often described more as a true partnership than one where the principal guest conductor has little or no say in artistic decisions.

“That’s most certainly not the case here, there’s no hierarchy,” Runnicles said.

There may not be a pecking order, but each man brings something a bit different to the working relationship, with Runnicles steeped in opera (he was the longtime music director of the San Francisco Opera) and Spano in the orchestral tradition.

“But we’ve branched out into each other’s territory over time,” Runnicles said. “We’d wanted to make it clear that we’re not stereotypical.”And Atlanta audiences will have at least another two years to experience their deepening collaboration.

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Concert previews

Atlanta Symphony Orchestra

“Symphony No. 3/Eroica” by Beethoven and “Violin Concerto” by Benjamin Britten, with principal guest conductor Donald Runnicles.8 tonight, Saturday-Sunday. $21-$79. Atlanta Symphony Hall, 1280 Peachtree St. N.E., Atlanta. 404-733-4900, www.atlantasymphony.org.

“Symphony No. 2/Resurrection” by Mahler,with principal guest conductor Runnicles, soprano Nicole Cabell and mezzo-soprano Kelley O’Connor, with the ASO and the ASO Chorus.8 p.m. Jan. 26, 28. $21-$79. Atlanta Symphony Hall, 1280 Peachtree St. N.E., Atlanta. 404-733-4900, www.atlantasymphony.org.