In added time at the end of the first half Eden Hazard was chopped down by Maya Yoshida, giving the 'blues' a free kick in a dangerous position.
Willian hovered over the set-piece but it was Alonso who stepped up to curl the ball round the wall and into the far corner.
It was a fine effort from the Spaniard, though question marks could be asked about Fraser Forsters goalkeeping.
Check out the goal for yourself below:
ALONSO GOAL 1-0!! pic.twitter.com/9z0W88WdAR
— CM (@ConteMindset) 16 December 2017