The Briton, who admitted he was "not a morning person", conserved as much energy as possible with Friday's final in mind, easing up on the last lap to come home safe in fifth place.
Farah, who claimed 10,000m gold on Saturday, is looking to become only the second man ever after Ethiopian great Kenenisa Bekele to win both long-distance titles at the Olympics and the Worlds.
He revealed the 10,000m final was tougher than he thought it would be, and was content to do the bare minimum at the Luzhniki Stadium this morning to keep his body fresh for another medal bid.
He sat in third or fourth for most of the race before moving to the front on the third to last lap.
As Ethiopian heat winner Muktar Edris and two Kenyans moved past him, looking to finish strongly, Farah had more to lose than gain by responding and eased over the line in 13 minutes 23.93 seconds, just behind American training partner Galen Rupp.
Farah and Rupp are the only two athletes going in the 5,000m who also ran the 10,000m.
"That was all right," he said. "I just wanted to do as little work as possible to be fresh in the legs, ready for the final and I did that.
"I've just been resting up (since the 10,000m). This is just the prelims and it's always going to feel harder as you've got to get up in the morning. I'm not a morning person and I had to get up this morning at six o'clock. You've got to get it out of the way and get to the final."
Farah had a rather unorthodox warm-down after his 10,000m victory, having to have his massage on a portable table under a tree outside the stadium after being denied access to the recovery area.
He added: "Galen and I looked across (on the home straight) and the top five qualify, which we were going to do. So I said save as much energy as you can.
"I wanted to run comfortably and not sprint all out and tire myself out for the Friday."
Kenya's Edwin Soi, the only man to beat Farah over the distance this year, finished ahead of Farah in second, while Ethiopian pair Hagos Gebrhiwet and Yenew Alamirew finished first and second in the other heat, setting up a mouth-watering final.
Gebrhiwet revealed, though, he also missed the race after getting on the wrong bus from his hotel, arriving at the stadium too late for a proper warm-up.
While Farah was gearing up for his second title bid, Katarina Johnson-Thompson, Great Britain's heptathlon hope in the absence of the injured Jessica Ennis-Hill, suggested it may not be too long before she is ready for one of her own.
Two personal bests this morning, 6.56m in the long jump and, even more impressively, 40.86m in the javelin, more than two metres further than she has thrown before, lifted her to fifth place.
It meant that, with only the 800m to come tonight, the Liverpool athlete, whose target had been a top-eight finish, lay on 5450 points, 42 off the medals.
She also has a far superior 800m personal best to Holland's Dafne Schippers, who sat third, and France's Antoinette Nana Djimou in fourth, but Germany's Claudia Rath, currently sixth, is on paper likely to edge her out in the fight for bronze.
Johnson-Thompson goes into the final event needing to finish within 0.3secs of Rath, just six points behind her, to get on the podium, but the German's best is more than two seconds faster than the Briton's.
Elsewhere, Robbie Grabarz, the Olympic bronze medallist, enjoyed a flawless high jump qualification, with his 2.29m clearance booking his place in the final on Thursday.
The 25-year-old has struggled in a tough follow-up season following his breakthrough last year.
He said: "It was really nice to come out today and qualify strongly.
"It's been a c*** season really, but I've had to be patient and we'll see what happens on Thursday."