Yes you do, because it it the affirmative "plus" (=more)
Read more here: http://french.about.com/library/weekly/aa101300v.htm
I'm not quite sure whether I completely got it, but here is what I've gathered:
1) If 'plus' is affirmative then it is [ploos], essentially when one means more of something.
Je veux [ploos] de quelque chose.
J'ai gagné [ploos] que toi.
2) If 'plus'is negative then it is [ploo].
Je ne veux [ploo] de quelque chose.
Je n'ai gagné [ploo] que toi.
3) If 'plus' is followed by an adjective or an adverb it is [ploo] unless it is followed by a vowel in which case a liaison is formed.
Je suis [ploo] grand que toi. (grand = adjective)
Tu cours [ploo] vite que moi (vite = adverb)
C'est [ploo-Z-] important que ça (important = adjective)
So even though 'plus' is affirmative - I am bigger than you and have 'more height' than you - 'plus' is pronounced as [ploo], because in this case it is followed by 'grand', which is an adjective.
Am I correct in my understanding?
You have missed something:
-je n'ai pas gagné [ploos] que toi is comparative (plus que = more than), even though the sentence is negative.
-if plus is followed by any word starting with a vowel or a non-aspirated H, the liaison will be Z :
C'est plus important/habituel [plooZ] - comparative
Je n'ai plus assez d'argent [plooZ] - negative
Thank you for your help, I really do appreciate it. One last thing regarding this 'plus' business:
Is there a difference between these two sentences or is my example simply wrong?
1) Je n'ai gagné [ploo] que toi. (my example)
2) Je n'ai pas gagné [ploos] que toi. (your example)
I can see the different wording, but do they mean the same thing? Is the 'pas' compulsory? Or are these just different ways how to express the same idea?
To be absolutely sure that "aime" is not understood as "love", you would have to paraphrase the sentence with something like: J'ai plus d'affection pour vous que lui, Je vous apprécie plus que lui.
Also "bien plus" usually means "much more", so "Je vous aime bien plus que lui" can mean "I love you much more than him".
This is where the French is not translating into a recognizable English as it is used by native English speakers would never use the word love when contrasting and comparing two individuals. It would always be "I like you more than him." And the translation given in DL for the word is to like. Either should be accepted