It looks nearly certain at this point that Rubio will beat Ted Cruz for second place in South Carolina by about 1,000 votes. This is, essentially, a tie for the two candidates, and both campaigns have spin for why that means it is a loss for the other side.
Team Cruz spins this as a loss for Rubio because he still hasn't won a single contest, and because he was able to parlay all his massive momentum into a bare bones win over Cruz. Team Rubio spins this as a loss for Cruz because South Carolina was supposed to be much friendlier territory to Cruz, with its very high evangelical population.
The more important spin is not about how the candidates actually fared in South Carolina, but the pitch they will make about how they can fare moving forward. Rubio voters will say, "If Cruz cannot beat Trump (or even Rubio) in South Carolina, where can he beat Trump on Super Tuesday?" The Cruz voters will retort, "Cruz is the only candidate in this race who actually has beaten Trump in a contest, clearly he knows how to get it done."
For this reason, Nevada may prove to be an even more important contest than South Carolina. If Marco Rubio is able to score a convincing second place finish over Cruz in Nevada, that lends credence to his national appeal and solidifies the narrative that he is building momentum. If it ends in a virtual tie again, on turf that is basically home field for Rubio, then Cruz can paint Rubio as a candidate with field of clay.
In the end, we may not know the truth about the post-race spin on this one until Tuesday night, after the results from Nevada come in.