No wonder Pep Guardiola regards Liverpool as being the proverbial pain in the backside.
The Manchester City boss was soon drawn to Jurgen Klopp’s side when asked earlier this week which teams could threaten his hopes of Champions League glory.
And it didn’t take long for the mixture of admiration and playful exasperation in Guardiola’s tone to be entirely justified.
While City romped home at Sporting Lisbon in ominous fashion on Tuesday evening, 24 hours later Liverpool were securing an impressive away result of their own – albeit in altogether different circumstances.
The manner in which the Reds took control of their round of 16 tie against Inter Milan in the San Siro demonstrated the qualities of which Guardiola is all too aware.
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Persistence, for one. A dogged self-belief. And, of course, the ability to solve problems on the fly to get the job done.
Liverpool were not at their best in Italy. Far from it. But that comes with the territory as the campaign starts to round the final bend before heading into the final straight.
With so much to play for, teams cannot be expected to rock up at accepted cathedrals of football and cruise to victory.
In fact, even a venue as relatively unassuming as Turf Moor can prove hugely testing with the result an increasing imperative, as Klopp’s side discovered at the weekend with the slog at Burnley.
There they ultimately won the arm wrestle before holding on to a victory earned by a goal from a corner.
They followed the same pattern at Inter, although the route travelled during the game was markedly different with the Serie A champions dominating for significant periods, particularly after half-time.
But Liverpool just wouldn’t yield. And with their strength in depth allowing Klopp to make the second-half changes that reshaped and revitalised the midfield, the Reds’ sheer relentlessness, durability and versatility eventually broke both Inter and their vociferous support, highlighted by silence that met Roberto Firmino’s opener but for the 2,100 travelling fans high in the stand in front of which the Brazilian scored.
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Yes, Liverpool have frittered away too many leads this season, a failing that may prove the difference with City in the battle for the Premier League title.
But the mentality monsters have long regained their bite. There’s a reason why. since the 3-1 defeat at Real Madrid last April that led to the Champions League elimination at the quarter-final stage, Liverpool have lost only two of 47 games in all competitions.
That run has included seven straight victories in Europe, the club’s best ever sequence not including penalty shoot-out triumphs.
The Reds have this term now won at the Wanda Metropolitano, the Estadio do Dragao and twice at the San Siro. Throw in comprehensive victories at historically difficult domestic venues Old Trafford, Goodison and Elland Road, and rarely can a Liverpool team have been so dominant, so overwhelming on their travels.
Klopp’s side, though, will now hope to harness the power of Anfield – and Anfield South – to maintain their four-pronged challenge over the coming weeks.
Five of the next six games are at home, with the other being the Carabao Cup final against Chelsea at Wembley on Sunday week.
Norwich City visit in both the Premier League and FA Cup, Leeds United and West Ham United are entertained in the top flight with Inter due for the return leg on Tuesday, March 8.
Klopp was quite rightly at pains to state the largely impressive display from the Italians means they will remain a threat at Anfield.
History, though, suggests why Liverpool are now strong favourites to progress to the last eight.
Ten times the Reds have won an away first leg in European competition by two goals, and on each occasion they have safely negotiated the return.
Six were by a 2-0 scoreline, the other four all 3-1 victories. There is, though, a warning it may not be entirely straightforward, with Liverpool having frayed Anfield nerves by losing the home leg against Roma in 2001 in the UEFA Cup, and in successive Champions League qualifying play-offs against Grazer in 2004 and CSKA Sofia 12 months later.
Inter, though, have now discovered what Guardiola has long known. Liverpool are that nagging discomfort that simply won’t go away.
