​An already tight race in north-central riding of Calgary-Klein now has one fewer candidate in the running.

The Green Party's Noel Keough surprised the crowd that had come out to watch an all candidates' debate Wednesday night with his announcement that he will now support his NDP rival.

"With a heavy heart, but a firm conviction in my decision, I am stepping out of the race immediately and putting my full support behind the New Democratic Party and their candidate Craig Coolahan."

A poll released last week by Abingdon Research suggested incumbent Tory Kyle Fawcett is in third place behind the Wildrose's Jeremy Nixon and NDP's Coolahan in the race for Calgary-Klein.

Keough says he and his party decided he should leave the race to limit vote-splitting among progressive voters.

"The policies of the NDP are not in perfect alignment with the Green Party but they are the most closely aligned. A win for the NDP in Calgary-Klein will advance Green principles and will make Alberta a better place to live."

Keough says he will try to have his name removed from the ballot.

Noel Keough, right, received a round of applause after announcing that he was dropping out of the race to support the NDP's Craig Coolahan. (CBC)

"Otherwise we will do everything we can to ensure people know that I'm no longer standing for election," he said.

Coolahan says he was surprised by Keough's decision to drop out.

"But, as he said, he's doing what's best for the riding, which is to send a progressive voice to the Legislature," he said. "And the NDP has the best chance of winning this riding."

Fawcett said the NDP platform is anti-oil and dangerous to Alberta's economy.

"We need to continue to work on improving our environmental record, but not at the expense of jobs for Albertans," he said.

Fawcett defeated Wildrose candidate Jeremy Nixon by 1,105 votes.