Toro Rosso's F1 season "deeply frustrating" so far

Key feels too many points have gone begging for him to be satisfied at the halfway point of the season.

Many have fallen by the wayside due to the early-season failings of the Renault engine, but some have also been due to mistakes of the team's own making.

"This season has been a mixed bag," Key told AUTOSPORT.

"The points we've scored still aren't very good, and there are lots of reasons for that, some of them outside of our control and it's deeply frustrating.

"That's what the season feels like - tonnes of potential, all looking good, what could go wrong?

"But then it just kind of unravels a bit when it matters and you turn around and say 'Well, how the hell did that happen?'"

Monaco was a case in point for Key as rookie drivers Carlos Sainz Jr and Max Verstappen qualified eighth and 10th.

Sainz, however, was demoted to the back of the grid for failing to stop when called to the weighbridge during Q1.

From such a positive position immediately after qualifying, Toro Rosso finished the weekend by claiming a single point for Sainz's 10th place.

"Monaco was unfortunate, and some of that was a little bit of pressure on new drivers at a tricky track for the first time where we missed a couple of things," added Key.

"We could've done a better job of supporting them with some of that.

"Monaco was a great opportunity. We missed that. We underperformed.

"Qualifying has been a little bit variable, and races too. Overall, we've only had one bad race and that was Bahrain."

With Toro Rosso just eight points behind fifth-placed Force India, the team's pre-season target is still in its sights.

Key said: "We just have to try and make sure we overcome these frustrations and then its possible.

"We will give it a damn good go, and if we don't achieve it we can say we had all the ingredients to have done so, but the textbook went against us."