COLOGNE, June 26, 2014 (AFP) - Willett had been forced out of Wednesday's Pro-Am as he struggled with a neck injury picked up while sleeping in Manchester Airport on Tuesday awaiting a flight to Cologne.
The 26-year-old then underwent extensive treatment to take his place on the same Gut Larcenhof course where he broke through two years ago to claim a maiden Tour title.
"I've had some terrible flights since taking two-and-a-half days to get back from the US Open so that's how I guess I picked up the injury but a round like this helps," he said.
"Also I was at Manchester Airport on Tuesday trying to catch up on some sleep when our flight was eventually cancelled.
"But the physio guys on the Tour have been great and with the weather pretty warm out here the neck hasn't felt all that bad."
Cabrera-Bello, who like Willett didn't drop a shot, had the encouragement of his younger sister Emma, who is a fellow professional and having competed on the Ladies European Tour from 2008 to last year.
"It's great having my sister here as she enjoys coming out a few times in the year to watch me play," he said.
"She's stopped playing full-time and is now a full-time student but we play a lot of social golf together, and we both try to help each other."
Seven players share third place on six under par including the England pair of Graeme Storm and Andy Sullivan, along with Northern Ireland's Michael Hoey, Frenchman Gary Stal, Denmark's Anders Hansen, Argentina's Emilano Grillo and Spain's Alvaro Quiros.
And Quiros also considered he was fortunate to take his place in the two-million-euro event having spent the past two days in bed nursing a heavy fever.
However, the six-time Tour winning 31-year-old was on top of his game in grabbing seven birdies and just taking one bogey as he looks to end a three-year winless drought.
"It was a very good day's golf considering I spent the last two days in bed," he said.
"My glands are still a bit inflamed and more lower back and neck hurt still a little bit but it's a typical sore body, and it was not to this morning that I decided I would play as I was seriously considering not playing.
"I even advised the European Tour I don't think I could play but this morning the fever I had two nights ago had broken, and on top of the warm weather we had today helped a lot compared to if we had rain and wind that would not have helped my body."
And reigning US Open champion Martin Kaymer struggled on the greens and also crowd expectation in his return to competition since his eight-shot Pinehurst triumph shooting a one-under-par 71.
"It was the best conditions we could get here, but I didn't make too many putts, especially over my last five holes, so it was worst I can do and unfortunately I just couldn't make the putts coming in, he said.
"But then the crowd support was fantastic and I was a little surprised how many people were here at 7.30 in the morning when we teed off, so tomorrow afternoon when I am out, it's going to be full.
"And coming back home the expectations from a lot of people, there are so many people that come out and expect you to play well and they expect you to play at least as good as two weeks ago.
"That's the way Germans are. But you have to lower your expectations and that makes it quite difficult.
"But then it's nice to be back playing here. But then at the same time is has been quite exhausting as there's been a lot to do."
Leading first round scores at the European Tour's BMW International Open at the par-72 Gut-Larcenhof course, Cologne on Thursday:
64 - Danny Willett (ENG), Rafa Cabrera-Bello (ESP)
66 - Graeme Storm (ENG), Alvaro Quiros (ESP), Danny Sullivan (ENG), Gary Stal (FRA), Michael Hoey (NIR), Emiliano Grillo (ARG)
67 - Shane Lowry (IRL), Romain Wattel (FRA), Nacho Elvira (ESP), Jorge Campillo (ESP), Branden Grace (RSA), Miguel Angel Jimenez (ESP), Tom Lewis (ENG)
68 - Andreas Harto (DEN), Carlos Del Moral (ESP), Robert Karlsson (SWE), Mikko Ilonen (FIN), Gaganjeet Bhullar (IND), Jans Dantorp (SWE), Matthew Baldwin (ENG), Kevin Phelan (IRL), Bernd Wiesberger (AUT), Henrik Stenson (SWE), Alex Cejka (GER), Ricardo Gonzalez (ARG), Anirban Lahri (IND), Soren Kjeldsen (DEN), Daniel Im (USA), Johann Carlsson (SWE)