With the altitude in Madrid, I wouldn't be surprised if it's his serve that is letting him down again
Yeah...and it seems Riba was serving very well, statswise at least.
It's an afterthought but maybe it was better if he played qualies, instead of getting WC into the main draw.
And in the next two weeks he will be losing many points from two challenger wins last year, so he will be ranked outside top 50 again.
Wish him better luck in Rome...