Elijah Page, 24, had asked to be put to death by lethal injection for the 2000 torture murder of a Spearfish man. It had been scheduled for 10 p.m.
Rounds and Attorney General Larry Long said that a 1984 law requires the state to use two drugs to kill a condemned person but that the standard now used is a three-drug combination.
Using the three drugs, as the state had planned to do, could have put the people who carried out the execution at legal risk, Rounds said.
The delay is in place until July 1, 2007, he said. That would give lawmakers time during the next legislative session to review the law and bring it into line with most other states that use lethal injection.
Rounds said he learned of the legal problem last week after reading an Aug. 14 transcript of a competency hearing for Page. Another death row inmate also raised the issue in June as part of his appeal.
Rounds said he asked for a review by Long, who didn't report back until Tuesday afternoon about five hours before the planned execution.
Earlier Tuesday, Rounds' spokesman had said the governor had no plans to step in. And the inmate himself had rejected pleas from friends and death penalty opponents that he reconsider as his execution drew near.
Page this year persuaded a judge to let him fire his lawyer and face the executioner for his role in the 2000 slaying of Chester Allan Poage, 19.
Page and two other young men killed Poage in Higgins Gulch in the Black Hills so that there would be no witness to the theft of a Chevy Blazer, stereo, television, coin collection, video game and other items from the victim's home.
As Poage begged for his life, the three men made him take off most of his clothes and forced him into an icy creek. They stabbed him repeatedly, kicked him in the head 30 to 40 times, tearing his ears off, and then bashed him with large rocks. He was also forced to drink a combination of drain cleaner and beer. The torture lasted at least two hours.
Page and Briley Piper, 25, pleaded guilty, and a judge sentenced them to die. Darrell Hoadley, 26, was convicted and sentenced to life in prison with no parole.
Page's case was considered unusual because a judge, not a jury, imposed the death sentence, because he asked to die, and because of his age. Death penalty groups said only seven people younger than 25 had been executed in the United States since the U.S. Supreme Court allowed capital punishment to resume in 1976.
The last execution in South Dakota was in 1947, when George Sitts died in the electric chair for killing two law enforcement officers.