The Country Fire Service sent 21 crews supported by six water-bombing aircraft to the fire north of Gawler on Friday.
They soon contained the forward spread, allowing authorities to reduce the threat level.
Another blaze burning at Midgee, on Eyre Peninsula, was also contained.
Emergency Services Minister Joe Szakacs said recent fires were an example of how quickly things could change and just how little warning some people might have to take action.
"During these hot days, the best thing people can do is be bushfire ready," he said.
The two fires came as SA sweltered through a fifth day of very high temperatures, the worst run of hot weather since December 2019, with the mercury climbing close to 38C in Adelaide.
Extreme fire conditions were declared across eight SA regions from Eyre Peninsula to the lower southeast.
That prompted the CFS to establish regional and state command centres, put incident management teams on standby and bring in extra aerial firefighting resources.
Despite the severe conditions, Chief Public Health Officer Nicola Spurrier said less than 10 heat-related cases had presented at South Australian hospitals in recent days, a sign local residents had heeded warnings to take care.
"I think we've all done a really good job. We haven't seen an increase in those presentations, our health services have functioned very well and I'm absolutely sure it's because South Australians have followed that advice that prevention is better than cure," Professor Spurrier said.
The SA Ambulance Service said while it had responded to a number of heat-related calls, including 35 on Thursday, the conditions had not prompted a major increase in overall demand.
Meteorologist Jonathan Fischer said while the heatwave was the first in some years, it was not uncommon.
"It is a fairly typical pattern for summer. We've had a couple of cooler summers so we haven't seen these longer duration heatwaves," he said.
"But what happens is when we get a high-pressure system sitting in the Tasman Sea and if it sits there for a number of days, the heat that is building up over the interior gets drawn down."
The conditions prompted authorities to activate heatwave emergency plans with community centres in Adelaide opened for rough sleepers as homelessness services conducted outreach programs around the city.
The Red Cross also provided free healthcare checks by phone, making more than 500 calls on Thursday.
The Bureau of Meteorology said a cool change sweeping across the state arrived in western regions early on Friday and was expected to reach Adelaide by late afternoon or early evening.
Milder conditions would then prevail for the next few days but the bureau was still forecasting a drier and warmer autumn across SA.
