Well, the title race is wide open now with Liverpool suffering their first loss of the season, that too at the hand of the current title holders, Manchester City. Let us analyse what went wrong for Liverpool today.
The match could be broken down into 3 defining areas:
A Tale of 2 Defenders
During the entire match, it was very apparent that City were bombarding through their left flank, with both of their goals coming down the left.
Which brings us to Dejan Lovren and Trent Alexander-Arnold: Trent struggled today and the defensive work put in by him was not at his usual best. Also, Leroy Sane's intensity was a bit too much for him on the day.

Lovren struggled today and even Virgil van Dijk drifted to the left flank at times to support. Lovren could have done much better defending against the first goal.
Midfield Battle
City were a different beast altogether in the midfield. Fernandinho showed everyone why he is such an important cog in Guardiola's system. He used constant pressure and great vision to push the ball up the pitch, instigating counterattacks whenever possible.

Liverpool's midfield were not able to string the passes required especially in the final third. They failed to provide the front three enough to create something to trouble Ederson.
The level intensity displayed by City was epitomized by the commitment of Bernardo Silva even at the dying moments of the game, and that showcased their desire. Liverpool, on the other hand, were sloppy, to say the least.
Attacking Threat
Liverpool lacked the creativity in the middle of the park and that left players like Mo Salah with little influence on the game. Also, the introduction of Shaqiri was a bit too late to achieve much.

Although the formation switch was made early on in the second half, keeping Wijnaldum on didn't help the case. Liverpool's best moments came when Firmino played the CAM role in 4-2-3-1 and that led to the solitary goal.
This leaves Liverpool with 4 points ahead of City and the title race is just getting more exciting. There is much for Jurgen Klopp to think on and maybe there is some room for January additions to be made.