Diggins said after the sprint yesterday that she wasn't in such good form atm. My guess is that that's to do with this being a Nordic Worlds year, last year there were no championships so the season-long goals were the World Cup and the Tour de Ski, both of which she won.
She could still win this or at least podium if she is good enough on the last hill (she's working really hard to catch Johaug and Weng now, but from a group with the likes of Andersson and Laukli she'd have to screw up pretty bad not to win the sprint).
Edit: alright, Sundling is going with her, that changes things in terms of the fight for the win as Diggins will need not only to catch the Norwegians up front (which she's doing a good job of so far) but also try to get rid of Sundling up the hill.
OK, so despite Johaug's efforts on the big climb to the timing marker, Sundling's got them back on. Diggins able to glide longer on the downhill, as usual the American skis working well on the downhill, but she's struggling to stay on the other three on the uphills and having to work hard to get back on time and again.