When Roma were announced as Liverpool’s Champions League semi-final opponents, many Reds fans breathed a sigh of relief. They had, after all, avoided German title-holders Bayern Munich and reigning European champions Real Madrid.But there’s no room for underestimation here: the Italians have been in outstanding form on the continent. After topping a group containing Chelsea and Atletico Madrid, Roma made it past Shakhtar Donetsk before humbling Barcelona in the quarter-finals.They will present a genuine challenge to Jurgen Klopp’s side when they meet in what should prove a fascinating encounter. Here are five things Liverpool should look out for...1. High line could make or break tieDefensively, Roma have made serious improvements this season. Francesco Totti’s retirement last year may have hurt, but a resolute collective has been formed in the iconic fantasista’s absence. They now fade less frequently, and are capable of keeping clean sheets even when faced with the finest forward lines.Their second leg against Barcelona acted as evidence of this newfound mentality and organisation. After Roma lost 4-1 in the Camp Nou, most assumed the tie to be over and done with. But, thanks to an extremely aggressive pressing game, and support from a high defensive line, the Giallorossi were able to score three without reply to send the Catalan giants packing.Statistics offer evidence of Roma’s solidity without the ball. No team in Italy’s top flight interrupts opposition build-up play more than they do, while only Napoli and Juventus concede fewer passes within 20 yards of their own goal. Put simply, it’s very hard to create real scoring chances against them.Liverpool could provide the sternest test yet of their high line. Mohamed Salah and Sadio Mane’s pace on the counter-attack can cause problems, but their difficulty here will be finding the time and space to run at their opposite men. If they get into decent one-on-one situations, they may be able to shift the tie in Liverpool’s favour.2. Alisson the sweeping supremoOne obvious route of attack for opponents lining up against Roma is to simply knock the ball long over their high line. However, the chances of this leading to genuine opportunities are reduced significantly by Alisson's presencebetween the sticks.The 25-year-old took over first-choice duties following Wojciech Szczesny’s departure for Juventus last summer, and has since established himself as the best goalkeeper in Italy. For those impressed by Ederson’s form for Manchester City this term, it’s worth noting that Alisson is ahead of him in Brazil’s pecking order.Roma’s shot-stopper is about so much more than stunning reflex saves – he’s a true sweeper-keeper. He relishes his involvement in building attacking moves, possesses the ingenuity of a playmaker, and is quick off his line to foil opposition attackers.Alisson’s importance is demonstrated by the fact that his team’s xGA (Expected Goals Against) in Serie A this season is 34.84, but in reality they’ve actually only shipped 27. If Liverpool’s attackers are to get past him, they’ll have to be precise in everything they do.3. Di Francesco, Italy’s up-and-coming tacticianEusebio Di Francesco’s coaching credentials were bolstered by his immensely successful spell with Sassuolo, during which he led the club from Serie B to the Europa League while playing attractive football. Given that he also made over 100 appearances for Roma – and won the Scudetto with them in 2001 – he was an obvious choice to succeed Luciano Spalletti last summer.Since taking charge he has surpassed expectations. While his Giallorossi outfit are capable of free-flowing attacking play, they are also a lot stronger than they were before defensively. That is largely down to Di Francesco’s tactics.The 48-year-old has kept opponents guessing in his maiden campaign at the Stadio Olimpico, showing versatility to move away from his favoured 4-3-3 and go to a 3-5-2 for the clash with Barcelona. That modification was key to his team’s high-pressing approach that suffocated the La Liga side.That performance cemented Di Francesco’s status as the latest top tactician to emerge from the peninsula, and has led to reported interest from Chelsea. Liverpool will have to be wary of his proclivity for changing things up.NEXT: Familiar faces in tow...4. Beware, the Premier League cast-offsOn paper, Liverpool may find reason for optimism when looking at Roma’s first-choice XI, which features three players not considered good enough by Premier League clubs over recent years.Edin Dzeko and Aleksandar Kolarov were both allowed to leave Manchester City, while centre-back Federico Fazio is hardly remembered fondly at Tottenham. But this trio should not be ignored – each, in their own unique way, play an important role for Roma.Fazio has evolved into a commanding defensive leader whose aggression and timing have helped him overcome a speed shortage; Kolarov offers pinpoint left-footed crosses and danger from long range; while up front, Dzeko could be integral to the Italian side’s chances of progress.Liverpool are one of the best pressing teams in Europe today. They make it difficult for opponents to play through midfield, congesting space and using turnovers to launch instantaneous counters. But with Dzeko an effective outlet, Roma can simply bypass midfield altogether with a ball over the top to their centre-forward, whose hold-up play is superb.5. Ünder could steal Salah’s thunderWhether or not Cengiz Ünder starts against Liverpool is dependent on what system Di Francesco goes with. If he opts for the 3-5-2 that downed Barcelona, the Turkish winger can expect to be on the bench. However, he will almost certainly enter the fray at some stage, and when he does he’s likely to pose a threat.This is the 20-year-old’s first campaign in the Italian capital, but he has quickly asserted himself as a big-game player. His away goal against Shakhtar helped Roma through to the Champions League quarter-finals, where he proceeded to set up Kostas Manolas’s tie-clinching header against Barcelona.Tricky and aggressive on the ball, Ünder is gradually filling the vacancy left by Salah on Roma’s right side. He will be aiming to go one better by taking the spotlight away from his predecessor when the two teams meet.New features you’d love on FourFourTwo.com
