After suffering a nightmare 2013 campaign the British-based squad appeared to have turned the corner this season, with both drivers scoring podium finishes at the opening race in Australia.
But since then the team have dropped down the order, taking sixth (Button) and ninth (Magnussen) in Malaysia before failing to register points in Bahrain and China. That run continued in Spain yesterday, with Button 11th and his team-mate 12th.
“The start and the first lap cost me a lot of time, and my second pit-stop compromised my strategy,” admitted Button, who was eighth on the grid.
“During the first two stints it felt like we were making progress, because we were faster than the cars in front.
“But we gambled on taking the second stop early, thinking we could jump one of the Force Indias, but Daniil’s [Kvyat] Toro Rosso followed me in, and caused my release to be delayed by a few seconds while he came past me in the pit-lane.
“Then I came out of the pits just in front of Lewis [Hamilton], who was lapping me. He was running old tyres, while I was on fresh rubber; I had to let him past, but it delayed me a bit more.”
Button remains positive however, concluding that “the midfield is extremely close, so even small improvements will make a difference.”
Meanwhile, Magnussen started 14th after a disappointing qualifying, then made a strong start only to run wide battling his team-mate.
“Today was pretty hard work,” reflected the Dane afterwards. “I made a good start, and was having a really good first lap. Then, into Turn 13, I went side by side with Jenson and went wide onto the marbles.
“As I came back onto the circuit, Sebastian [Vettel] hadn’t seen me, and our cars briefly touched. Luckily, there was no damage to either of our cars, so we could both carry on without problem.
“I knew it would be difficult to go forward from 14th on the grid – the midfield is very tight, so making progress is extremely tough."
Magnussen also suggested that his qualifying result cost him dear come the race.
“If we’d started where we should have, I think we could have scored some good points today. As it was, there wasn’t much we could have done out there other than what we did.”
The team will be hoping for improved fortunes at the upcoming Monaco Grand Prix. Button enjoys an impressive record in the Principality, having won for the Brawn squad in 2009 and taken further podiums in 2004 and 2011 for BAR and McLaren respectively.