It was a pretty straightforward trading day considering what's at stake in the bigger picture.  Bonds were under slight pressure overnight, but were only slightly weaker in response to more pronounced weakness in Europe.  That changed after the ISM Services data came out.

The report was much stronger than expected, with the headline PMI rising at the quickest month-over-month pace in the history of the report!  Bonds immediately sold-off.  Treasury yields flirted with 1.73%--part of a dangerous "ceiling zone" that stretches up to 1.75%.  

MBS lost enough for several lenders to reprice negatively, but then began to outperform relative to Treasuries.  In fact, heading into the close, MBS made it back to 'unchanged' on the day while 10yr yields were still nearly 2 bps higher.  The video discusses the outperformance in greater detail.