Suggestions to work with rivalry coworker

[Anonymous]

I have a colleague who seems to frame me as his rivalry.

We were both hired recently and were assigned to work on similar (sometimesoverlap) projects. Since I came onboard 1 month earlier than him, the boss told me to "lead" a small project that we two were supposed to work on together.  In front of the boss, the colleague would agree with my proposal, but when we two need to work together, he would have hundreds of reasons why this would not work, that would not be good, etc. When I ask for his ideas, he flips all the time. Basically, he just refuses to work.

Honestly,I don't mind if I'm the "lead" or not, as I can see his reluctance to be "led" by his peer (or maybe his inferior). But the work needs to be done. What's your suggestion for me to approach it?  I imagine that if we include the boss in all our meetings (i.e.,at least superficially make it a work led by the boss), the colleague would come along, but that seems like a lot of use of the boss's time and effort. I don't mind framing it as this colleague is leading me, but don't know how to bring it up without accusing him of being uncooperative. Or I could try to do it myself, which risks being attacked by the colleague for not agreeing later on. I'd love to know your suggestions!

[Anonymous]

Document all decisions and follow up assignments from meetings with boss, then assign specific items to your colleague with delivery dates. Then send status updates periodically to boss with a running list of pending items. If there are incomplete items assigned to your colleague and past due, it will reflect on them