Has Liverpool's attacking trio actually regressed since last season?

As Mohamed Salah, Sadio Mane, and Roberto Firmino trudged off the Parc des Princes on Wednesday, it was difficult not to recall the contrasting, ebullient moods of last season.

During the 2017-18 campaign, Liverpool comprehensively dismissed FC Porto, Manchester City, and Roma en route to the Champions League final, with the cohesive trio's pace and ruthlessness delighting viewers across the continent. Now, after suffering defeat to Paris Saint-Germain, the Reds are on the verge of group-stage elimination.

In the Premier League, Liverpool are valiantly keeping pace with Manchester City, but the victories haven't been as overwhelming or convincing. Slender one-goal wins are more commonplace.

Have Liverpool's fab three lost their spark?

Here, ahead of the Reds' visit from local rivals Everton on Sunday, theScore assesses Salah's, Mane's, and Firmino's league statistics to definitively answer oft-aired assertions that they've gone off the boil.

General productivity

In the 2017-18 Premier League season, the three-pronged frontline scored over two-thirds of Liverpool's goals. Even when Philippe Coutinho left for Barcelona in the January transfer window, their potency didn't relent: midfield tussling from the likes of Alex Oxlade-Chamberlain and James Milner wrung out chances, while Trent Alexander-Arnold and Andy Robertson were increasingly influential from either side of the back-four.

Liverpool were a delight to watch but, if you look into the numbers from the artillerymen in the opening 13 matches of the 2017-18 and 2018-19 terms, the general productivity is identical.

Opening 13 matches of 2017-18

Opening 13 matches of 2018-19

Mane has covered some of Salah's workload, but the overall output is the same. Rather than someone starring individually, there is presently a more collective attacking effort in Jurgen Klopp's third full season in charge.

Situational statistics

Looking into the situational statistics of the trio's goals provides an insight into the kinds of chances being created.

Among Liverpool's top creators are Robertson and Alexander-Arnold with five assists between them. The doubled number of goals scored from close range this season would suggest the trio have feasted on the youngsters' whipped crosses, or preyed on spills and scuffs from goalkeepers and defenders.

Opening 13 matches of 2017-18

Opening 13 matches of 2018-19

The explanation for a slight dip in Salah's productivity appears simple: While many Liverpool supporters would blame his infamous tangle with Sergio Ramos in May's Champions League final, it is more likely down to defenses growing more adept at preventing him from drifting inside the penalty area and onto his stronger left trotter. Further pawing over Salah's numbers during the opening 13 matches of the past two seasons reveals his goal tally with his left foot has taken a minor hit from seven to five.

Expected goals

Expected goals data may irk some football purists, but it has worth. The advanced metric was created following analyses of countless football matches and thousands of shots, determining how likely a player is to score in each scenario. For example, a high-quality chance like an open goal from six yards would have a value very close to one, while a shot from 35 yards in front of a thicket of opposition players would have a value close to zero.

The overall number of expected goals (xG) for each player over the opening 13 matches isn't vital - Liverpool's frontmen have collectively played in 728 more minutes this season, so the numbers in the 2018-19 xG column should be higher - but the comparison between the xG and actual count of goals is important. xG per 90 minutes is also helpful as it simply determines a player's likelihood of scoring in a full match.

Opening 13 matches of 2017-18

Opening 13 matches of 2018-19

There is a five percent dip in Salah's chances of netting in a Premier League match, while Mane's chances of scoring are nearly the same as the prior term - his actual goal count is partly helped by appearing four more matches than at the same juncture of last season. The biggest difference is seen in Firmino: according to the statistics, he has been the beneficiary of slightly better opportunities than Mane but has half the goals of his Senegalese teammate.

Analysis

The primary reason for the claims that Liverpool are losing their attacking zip is obvious: Salah's mild slump in potency. By this point of last season, the Egyptian was firing and still getting better. Mane has helped cover much of the dearth with an excellent opening third of the season, but Firmino - while starting at an identical scoring and assist pace as last season - could be doing a little more.

The forwards are offering the same output but, given the chances they've carved out for themselves, they could have done even better through the opening 13 games of the last campaign.

And that's exactly what they're doing: carving out chances for themselves. Perhaps the focus of creating opportunities is too centered on Robertson and Alexander-Arnold. The likeliest reason, though, is this season's slightly softer press from the midfield - Milner, Georginio Wijnaldum, and Jordan Henderson are all attempting fewer tackles - is resulting in fewer turnovers in advantageous positions and, therefore, fewer key passes coming from the front three's colleagues.

Key passes from rest of team

That penetration and bite from the middle will likely improve as Naby Keita and Fabinho settle into life on Merseyside and allow the likes of Milner and Wijnaldum time to recuperate. But for now, the backing brigade aren't loading ammunition into the front-line weaponry at the same rate.

However, Liverpool fans should brush criticism aside. Although the Champions League campaign is in severe threat, the Premier League conquest is alive and well. At this point of last season, Liverpool were sixth and already 14 points short of Manchester City. Now, prior to Sunday's Merseyside derby, they are just five points adrift of Pep Guardiola's rapacious roster with a game in hand.