Jenson Button has described his Mexican Grand Prix as 'painful' as McLaren-Honda's top speed deficit was again made plainly clear down the home straight at the Autodromo Hermanos Rodriguez, even if he remains encouraged by the chassis potential.

Starting from the back of the grid after failing to make it out for qualifying, though Button fared better than team-mate Fernando Alonso - who retired on the opening lap - by reaching the chequered flag, he was never in top ten contention.

Made to look particularly slow down the 1.2km home straight, as cars behind used DRS and deployment to ease past with a '45kph advantage', Button says McLaren-Honda's work is far from done.

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"[The race was] Painful," he said. "I was on the harder on the start but it was just waving goodbye to everyone at the start. The straight line speed they have is phenomenal. We are still doing 345kph on the straight, but they are 20kph quicker than us. So when they have DRS and full deployment they are 45kph quicker than us.

"It is a massive difference in speed, I couldn't hold people behind me even if I was in front of them, not that was very often unless they were pitting or lapping me. We have a lot of work to do."

Despite this, Button did take some positives from the car's performance in the twisty sections of the track, saying he was passed by a Williams at the end of the home straight and was able to keep up until they came back around again.

"The interesting thing is, compared to a Williams or the middle of the pack cars we are quicker in the last sector. The last sector is unbelievably slow, but the car was working better there.

"When Bottas lapped me, I dropped back 1.5secs then caught him for the DRS zone. Those sort of sectors the car is working pretty well."