I don't understand why people think that Luffy can suddenly defeat Lucci if Usopp motivates him.
Luffy was fighting with the knowledge that his entire crew would be assassinated in the event of his own defeat.
I remember the fight between Luffy and Don Krieg, and specifically I remember Zeff saying that the person who 'wanted it more' would win. In every fight so far, Luffy has 'wanted it more' than his opponent.
In this fight, I don't see that as being the case. Luffy no longer has that advantage, further, Luffy is physically inferior to Lucci.
Luffy lost his fight with Aokiji because he lacked strength, so Luffy developed new technique to deal with this problem. He lost this fight because he lacked endurance.
It was stated somewhere that this was the concluding chapter of the fight, why would they blatantly lie just to create tension? Usually, they'd state it as a question if it weren't actually the last chapter of the fight. "Is this the end of the fight!?" not, "This chapter concludes the fight."
Just as Luffy could not kick Aokiji's ass even if Usopp screamed to him with the same magnitude, Luffy cannot kick Lucci's. I won't say it's impossible though, since this is Oda we're dealing with, so Luffy might just ressurect and go super saiyan, I guess.
Still, I think it's more likely that Usopp will do something to save Luffy (NOT kick Lucci's ass, though), and it's very possible that now that Lucci defeated Luffy, he will collapse as well, or at least be unable to assassinate Luffy's crew due to the injuries he recieved.
Which will mean that Luffy's talk about protecting his crew was not bullshit.