1. Bristol City stun holders United

Bristol City stunned Manchester United by knocking the Carabao Cup holders out of the competition and sealing a place in the semifinals with Korey Smith scoring a dramatic winner, two minutes into stoppage time for the Championship outfit.

United, who won the cup against Southampton at Wembley last season, had looked set to take the tie into extra-time after Zlatan Ibrahimovic's free kick cancelled out Joe Bryan's spectacular opener six minutes earlier. But despite dominating the closing stages, United were unable to score a second, and Smith secured a famous win for Lee Johnson's team at Ashton Gate by scoring with just one minute of stoppage time remaining.

United manager Jose Mourinho made wholesale changes to his team following the 2-1 win Sunday at West Brom, but his side contained internationals in virtually every position. But the home side, riding high in third position in the Championship, proved more than a match for United and deservedly claimed a place in the last four.

United's finishing was ultimately their undoing, however. Ibrahimovic and Marcus Rashford hit the woodwork in the first half, and more chances went astray after the break.

City proved more ruthless in front of goal and claimed the win that will go down in history at the club -- and prove to be a humiliating memory for Mourinho and United.

2. Zlatan nowhere near his best

Ibrahimovic will take plenty from his 69-minute outing at Ashton Gate, with the Swede making his first start and scoring his first goal since suffering a cruciate ligament injury against Anderlecht in April.

The 36-year-old has stunned United's medical staff with his return to action just seven months after sustaining the injury, with many not expecting him back until January at the earliest. But while he has proven his doubters wrong, Ibrahimovic will be the first to admit that he is still some way short of his previous sharpness, and that was evident against Bristol City.

The former Paris Saint-Germain striker had made little impact in his five previous appearances since returning from his layoff last month, but his ring rust is understandable. This game was his chance to step up his pursuit of full fitness, however, and he will only benefit from the workout.

His fitness will have been boosted, but his finishing and touch remain in need of work. A first-half effort that hit the post was wayward rather than unlucky, and Ibrahimovic's hold-up play was uncharacteristically sloppy.

But by scoring the free kick that cancelled out Bryan's opening goal, he got United back into the tie and did what he did so often last season by rescuing his team from a difficult situation.

By the time he was replaced by substitute Henrikh Mkhitaryan midway through the second half, Ibrahimovic had done his bit, but there is still more to come.

3. United continue to look shaky on set pieces

Bristol City boss Johnson pinpointed a recurring weakness in Manchester United's armoury by spotting the vulnerability of Mourinho's team when defending set pieces.

It is an unusual problem for a Mourinho team, with the Portuguese traditionally ensuring that his defenders know exactly what to do and when at corners and free kicks. But in recent games, United have been found wanting at set pieces, with both of Manchester City's goals in the 2-1 derby defeat earlier this month coming from a failure to clear a corner or free kick into the penalty area.

The same happened during Sunday's 2-1 win at West Brom, when more chaotic defending at a corner allowed Gareth Barry to score from inside the 6-yard box for the home side.

But despite the change in personnel for this game, United once again struggled to protect their goal as Bristol City tested them repeatedly at corners and with Hordur Magnusson's long throw-ins. Nobody in a United shirt was prepared to take responsibility when the ball came into the box, and the home side, sensing United's anxiety, continued to test them.

United weathered the storm on this occasion, but the secret is clearly out when it comes to their difficulties defending set pieces.