User blog comment:AYET/Will Luffy accept assistance/@comment-24769684-20150408143435

I indeed think that normally, Doflamingo would be much too powerful for Luffy, as Crocodile was in Alabasta. Look at how easily Doflamingo handled Luffy in their first battle in Chapter 745.

However, I'll borrow from Woohoot's comment here, in the battle in 745 Doflamingo hadn't activated the Birdcage yet and fucked up Dressrosa in general. He had beaten Law to a pulp and shot him, but Luffy did not witness that and so wasn't really sure why Law was a prisoner. In the end, Luffy did not really have a reason to fight in 745, and so was thrashed accordingly.

Also, before the events of the Dressrosa Arc, Luffy did not hate Doflamingo. He was just following Law's plan to destroy the SMILE Factory, defeat a Yonko, and help him become King of the Pirates. Doflamingo was not really on his hit list until he activated the Birdcage and attempted to kill his crewmates and assorted friends.

Now, however, things are different. Doflamingo is still clearly a powerful fighter who could easily fight on par with Luffy, if not outright defeat him again, but he's been weakened significantly by Law and his Gamma Knife. Now Luffy is fighting a man whose internal organs are massively messed up. So to answer your question, Luffy has already gotten assistance in this battle, and it will be the reason that he achieves victory. Any further assistance from, say, Sabo, would just be overkill.