Messi nonchalantly rolled his kick into the corner after Pedri had been fouled and despite having other chances they couldn't find a second goal.
And they were punished as Clement Lenglet's silly foul allowed Alex to roll home the spot kick and claim an unlikely and perhaps underserved point.
So who were the standout performers?
✔️ GOOD PERFORMANCE
Ousmane Dembele: 7.7
Once again, Dembele's action just at the end of the move remains wanting, but he's doing so much right up until that point.
In the second half he went on a mazy run, battering his way through the Cadiz defence but instead of shooting he cut back onto his left and his eventual effort was blocked.
Minutes later he marauded down the right flank but when the chance came to shoot he dragged his effort across the goal. Dembele's all-round play shows pace and stretches defenders, but if only he could get that final part right, he could be the player that Barca spent all that money on. And in the end it proved pivotal as Cadiz stole a point.
⭐ STAR MAN
Lionel Messi: 8.8
Even on what you would consider to be a low-key outing, Messi is still head and shoulders above every other player on the field.
As well as scoring from the penalty spot, Messi also hit a game-high seven shots, finding the target with three of them. Indeed he probably should have had a second but volleyed over the bar from close range in the second half.
Messi also completed three dribbles and created one Big Chance for a team-mate during the match. By his high standards he was reasonably quiet, but still did more than enough to put up a man-of-the-match performance. And yet it will be another frustrating evening after Cadiz stole a point at the death.