It is a sign of just how impressive Chelsea have been this season, that two games without a win have caused such concern. It is not so much for the results, though, but the manner and patterns starting to emerge.

In fact, extending that to each of Chelsea's last three games - a win over Brentford, draw to Everton, and now defeat against Fulham - there has been a similar theme. A first-half lead in two of those was followed by a significant drop off in intensity, quality, and control by the final 20 minutes.

More specifically, momentum appears to swing around the hour mark. It is at this stage (63 minutes for Brentford, 72 for Everton, and 67 for Fulham) that substitutions are made. However, the earliest Enzo Maresca has gone to his bench in the same fixtures is the 73rd minute.

That came in Boxing Day's late collapse. A leggy Chelsea team had struggled to truly assert themselves on tricky opposition at Stamford Bridge already but were still second to draw their gun even in a position of strength at 1-0 up. The change was a common one for Maresca, replacing the tireless but fading Nicolas Jackson with perennial second-choice Christopher Nkunku.

Outside of victory over Bournemouth in September, it isn't a switch that has brought about much reward. Nkunku does not favour being a lone No.9 and has rarely been able to make a positive impact. The same was true against Fulham as he hardly touched the ball and offered little of the tenacity shown by Jackson when pressing or competing for the ball.

In contrast, Marco Silva's first sub scored less than 10 minutes later when he acted to impact proceedings. Harry Wilson bagged his fourth of the season, all of those coming from the bench.

Gareth Southgate described changing the narrative of the non-starters whilst with England, terming them 'finishers' rather than substitutes. Chelsea, it seems, have not gone that far.

In turn, Fulham smelt blood as the direction of the match continued to go in their favour. Tom Cairney and Rodrigo Muniz came on. The latter would score the winner 20 minutes later, deep into added time, surging forward to get into the box as Chelsea legs chased back, extremely slowly.

By the time Muniz completed the turnaround, Fulham had replaced 40% of their starting outfield players. Chelsea had swapped only 10%. Four times less. Over a busy winter period, it certainly told.

This is a feature now starting to harm Chelsea and Maresca. At Everton, in a sluggish attacking performance but one with grit and fight elsewhere, only two subs were made. They came after 75 and 76 minutes with Nkunku, as ever, one of them. Sean Dyche made three of his own just moments earlier.

Neither side looked like pushing for three points at Goodison Park, regardless, with match conditions and Chelsea's poor record there playing into matters. It seemed to be a decent point but the seeds of issues which emerged against Fulham had been sown.

Maresca made one change to his starting XI between games, offering four days of rest to a group now accustomed to a full week due to the lack of Conference League commitments for many of them. He followed that up with a single substitution and was made to pay as Chelsea failed to match the energy shift and dynamism of their opponents.

The warning signs were there. In the win over Brentford, Thomas Frank made four subs just after the hour mark and saw his team fight back, hitting the bar and swarming Chelsea. Jackson's breakaway second ought to have sealed matters but a late Bryan Mbeumo goal made it nervy at the end.

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By full-time, with Chelsea hanging on, Brentford had used all five of their allowed changes with Chelsea making just one. It means that of the last 15 available to Maresca, he has only made four changes.

When asked on Thursday about the lack of subs, he gave somewhat of an explanation. “If you decide to put Marc [Guiu] in, you have to change one that is there, and we decided to change Nico [Jackson] for Christo [Nkunku],” he said. “Joao [Felix] has more or less the same position as Cole [Palmer]. In some games, they already play together, but it’s also a matter of balance."

Maresca can also say that his bench against Fulham was perhaps the weakest of the season with no Romeo Lavia, Reece James, or Mykhailo Mudryk to call on. Noni Madueke was left out for an unclear 'technical' reason, which further hampered things. Kiernan Dewsbury-Hall was injured but hasn't made the cut much this season, on this occasion neither did Carney Chukwuemeka. Cesare Casadei was left twiddling his thumbs again.

Many will reasonably argue that these players have little to offer, and may well be right, but with talent differential in the Premier League diminishing between the top and middle of the table, fresh legs are vital and Maresca has shown an unwillingness to use the fringes of his squad in the Premier League, even if it only meant adding speed and a rested body over a wilting one.

Conference League fixtures have provided minutes for those not deemed part of his true core, but those in a rotational position are not getting the action elsewhere that suggests Maresca really is happy with the quality and readiness throughout. This is not just a matter for the past two weeks, either.

Against Southampton in early December he waited until the 72nd minute to make a change despite starting Moises Caicedo in a match against the league's bottom-placed side. Caicedo would go on to finish the game whilst only three changes were made in total. Palmer hardly got a rest. Russell Martin's men had a player less for over half of the match, yet Maresca still showed caution in resting his key figures, even in a rotated side.

Similarly, it took until the 80th minute away to Leicester City before a quadruple substitution was made. That only came once Enzo Fernandez had doubled the lead and the total dominance reflected in the scoreline.

It will be no surprise, though, that Chelsea have conceded more goals (six) in the final 15 minutes of matches compared to the same time period throughout the rest of the games this season. In Brentford and Fulham, half of those have come in the last 10 days. It seems as though Chelsea's Premier League fatigue and lack of rotation is costing them as opponents adapt.

This is not wildly showing in the table as Chelsea still impress and outperform their relative rivals. It is something starting to crop up more as a problem, though, and at the worst and most demanding period of the season.

For Maresca, it is not a new point. His Leicester side in the Championship had the joint-third most unused substitutes in the division across 46 games last season. With five available, he averaged just over three per game, but it was a common gripe with supporters - especially in the second half of the campaign - that not enough were made and that they came too late.

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In particular, defeats to Plymouth and Leeds as well as a draw to Hull City stood out during a run which threatened to derail what looked to be a title cakewalk. There, Maresca made two changes whilst 1-0 down to Plymouth with his opponents completing four; at Leeds, he once more only turned to the bench for two subs (in one go) whilst fresher legs were introduced against him and a late comeback was completed; At Hull he also only went for two.

With this being the first full senior season he had overseen, Maresca's management across the course of nine months as opposed to the shorter and less intense academy campaign at Manchester City, came into focus. Leicester's slump was highlighted as a red flag for his fitness and rotation in the back end of 2023/24, and Chelsea will be keen to avoid the same happening to them.

It is ultimately only two games for Maresca, and he carries immense goodwill currently. Chelsea did not expect to be this high up the table or in such a commanding position over their Champions League-chasing rivals. Should he refuse to make use of his squad over the coming weeks - with a trip to Ipswich just four days after the Fulham match - then it will quickly become the biggest concern and red flag over his coaching so far.

For now it will remain a small thing but with the potential to grow. This is the first real on-field hurdle for Maresca to truly overcome with doubts emerging at a crucial time of the season. It may not prove to be much, but that is all the Italian has left to be properly criticised after such a fine start.