Dams driver Magnussen, a test driver for the McLaren F1 team, started on pole position and comfortably won the race by nearly 20 seconds from Strakka Racing's British driver Will Stevens.
France's Arthur Pic came thid in the AV Formula car, finishing right on Stevens' heels, with Russia's Sergey Sirotkin (ISR) fourth.
After earlier rain during qualifying the track had dried out by the time race start came around, polesitter Kevin Magnussen staying ahead of the field as the lights went out.
Jumping up from row three to second place at the first turn was Pic, while Sirotkin, Christopher Zanella (ISR), Marco Sorensen (Lotus), Norman Nato (DAMS), Stoffel Vandoorne (Fortec Motorsports), Nigel Melker (Tech 1 Racing) and Stevens completed the top nine.
Nico Muller (International Draco Racing) was the first to bear the consequences of some keenly contested exchanges in the bunch, the Swiss driver crashing out, while up ahead Magnussen quickly settled into a groove on the Spanish track, posting several fastest laps to take nearly a second a lap out of his closest pursuer Pic.
Among the leaders Vandoorne, Sorensen and Zanella all fell off the pace to allow Nato to move into fourth and take the attack to Sirotkin in third. Nipping past the Russian into second, the Frenchman then had to contend with the charging Stevens, who found his way past Sirotkin and into third. Not to be denied, the Briton caught Pic and slipped past him and into second on the last lap.
In a class of his own, Magnussen took the chequered flag by some 20 seconds from Stevens and Pic, with the remaining points placings being taken by Sirotkin, Nato, Melker, Zanella, Vandoorne, Sorensen and Mikhail Aleshin.
Kevin Magnussen was delighted: “It’s only the start of the championship but it’s still important to go out and score big. I had a very good car today and I made sure I didn’t make any mistakes.”
Will Stevens was thrilled to have come through the field: “I was disappointed with our results at Monza, and we needed to score points today. The car has a lot to offer in the way of performance, especially in the dry. I was able to attack throughout the race.”
Arthur Pic was happy to make the podium: “I’m very pleased for AV Formula, who were racing at home here. The stable did a lot of hard work this winter and we’ve made a lot of progress with the car’s race set-up. It’s a good result on a track that I’m especially fond of.”