MANCHESTER, England (AP) — Six months into the season, finally there might be a glimmer of hope for Manchester City's frazzled rivals.

A night that saw City secure its place in the English League Cup final — setting up the prospect of a first of potentially four trophies for the team this season — also highlighted a vulnerability in Pep Guardiola's side that has been noticeable since the start of the year.

In winning 3-2 at second-tier club Bristol City on Tuesday in the second leg of the semifinals, Man City's run of games without a clean sheet extended to six. A defense that looked so solid from August to December is starting to look frail, conceding goals from the few chances opponents are creating — just like last season.

It has coincided with John Stones' return to the team after 6 1/2 weeks out injured. The ball-playing center back had been widely praised for cutting out his individual errors before his layoff with a hamstring problem, but has been at fault for four of the 10 goals City has conceded in 2018.

The absence of a senior left back is also starting to tell. Since Benjamin Mendy got injured in September, midfielder Fabian Delph has filled in as an emergency left back and exceeded expectations. Yet injury has limited Delph to only one start in the six games in 2018, with Danilo — a right back — and youngster Oleksandr Zinchenko coming in.

That left-back area is City's clear weakness, with Mendy not expected to return until April at the earliest.

City has won five of those six games this year — the only loss being 4-3 at Liverpool in the Premier League — so its prolific attack has been masking the occasional flaws of the defense. Tougher tests remain for the team, however, particularly with the Champions League resuming next month.

"We lost control," Guardiola said after seeing Bristol City come from two goals down to pull level at 2-2 before Kevin De Bruyne's injury-time winner at Ashton Gate sealed a 5-3 aggregate win.

With an eye on City's last-16 matchup in the Champions League, Guardiola added: "Maybe it will be good for us, for the Champions League against Basel, to learn that you have to play for 90 minutes and anything can happen."

Guardiola's reported interest in Athletic Bilbao defender Aymeric Laporte, a France under-21 international, shows he is not satisfied with his four current center backs — Stones, Nicolas Otamendi, Eliaquim Mangala and Vincent Kompany. The first three were bought for a combined cost of about 120 million pounds ($170 million).

The injury-prone Kompany, meanwhile, was on the bench on Tuesday after recovering from his latest setback, an undisclosed problem sustained at Newcastle on Dec. 27. But it is becoming increasingly clear that Guardiola can no longer rely on City's club captain, a stalwart in the team since 2008.

Despite City's shakiness of late, don't expect Guardiola to waver on his utter commitment to attacking soccer.

"I'm not a coach for the tackles," Guardiola said after Manchester City's 4-2 loss at Leicester in December 2016, a remark used by some critics to underline misgivings at his ability to set up a defense.

Statistics show otherwise.

In Guardiola's seven years managing Barcelona (2008-12) and Bayern Munich (2013-16), his teams had the best defensive records in the league each season. Bayern conceded only 17 goals in Guardiola's final year, a Bundesliga record.

This season, City has the third best defensive record in the Premier League, conceding 18 goals in 24 games.

Still, there is always the risk of Guardiola's teams being exposed at the back, either because of his goalkeeper or defenders getting caught in possession or by opponents picking them off on rapid counter-attacks. The most striking examples of that are Real Madrid's mauling of Guardiola's Bayern in the Champions League semifinals in 2014 and Liverpool's harrying of City's defense at Anfield this month.

Left behind so far this season, City's opponents still have something to cling to.