Walker's form, stones at dm and two of the most important cogs of the team last season both in attacking and defensive workrate in de bruyne and d.silva not in the team means this was always on the cards. With that said besides their first goal which walker could've done much better, don't think the team has been particularly poor besides walker defensively. It's just that type of day where every shot the opposition takes goes the only place it can be a goal.
Drawing or even losing this game won't be the end of the world and anyone handing the title to liverpool if the desired result doesn't happen need to relax, there's a lot of football to be played. If the team does come back in the second half which I believe they can, then this will be the game and win that gives me even more confidence that the title will be retained. Especially with de bruyne and silva still to come back to full fitness and no fernandinho it will send a real message to liverpool and rest of contenders that this team means business so hopefully the players go out there the second half and show who they are.