Johnson was prepared to see how fourth-inning warmups went before making a move, but after seeing Strasburg up close, he made the call to the bullpen.
It marked the shortest outing of the season for Strasburg, who left trailing, 3-2, after three frames. Chien-Ming Wang entered in relief, and was given ample time to warm up.
Strasburg last threw so few innings Sept. 11, 2011, when he also went just three against Houston. He allowed only two hits Saturday, but gave up three runs (all earned) while walking four. He threw 67 pitches and also labored on the basepaths, recording a hit in the second and walking in the third.
"It's tough out there," Strasburg said. "Obviously, I wanted to go out there and compete. I expected a lot more out of myself. By no means was I going out there thinking I wasn't prepared for it. I did everything I could to be ready for it, as far as hydrating. You've just got to learn from it. It's a tough situation."
The San Diego native has had the misfortune of pitching in triple-digit temperatures in his last two outings. Before throwing in the sweltering Atlanta heat Saturday, he pitched in 101-degree temperatures a mile above sea level in Denver on Monday.
Strasburg said he did everything he could to pre-hydrate before the outing, but was sweating profusely out on the field, and Johnson said the hurler's blood pressure was "way up." He received three IVs of saline solution in the clubhouse after the game, after making every attempt to stay out of the heat in between innings.
"I think it was a great decision by Davey," shortstop Ian Desmond said. "You preach to kids, if you're hot and you feel dizzy, come out of the game. I knew a kid that died at a young age in Florida. He was hot, but he kept on practicing, and next thing you know, he was gone. So, for me, I was relieved that they made the right decision there and got Stras out."
The good news, Johnson said, is that Strasburg -- who could be selected to his first All-Star Game on Sunday -- should be able to recover soon.
"I talked to him after the game and asked him how he's doing, and he said he's doing OK," Johnson said. "The doctors are obviously going to monitor him and everything, but he was really dehydrated. It's serious, but it's not something you can't recover from."
Temperatures are expected to be in the triple-digits again on Sunday, which would mean thermometer readings above 100 degrees in each of the three games in steamy Atlanta this weekend. Other players have made a concerted effort to stay cool and prepare themselves for those hours out on the field, where the heat index climbs even higher.
"Clearly it was hot out there today, but I made some adjustments to my uniform and I was able to stay semi-cool," Desmond said. "I changed my undershirt that I normally wear ... and folded my socks down to let a little air breathe down there. It's really all you can do, to try to cool yourself off as much as possible."