The modern Champions League has not been a hospitable competition for underdogs. Real Madrid, Barcelona and Bayern Munich have won the last four trophies, and the closest thing to an upset winner in recent years was Chelsea in 2012. This season, though, might be different.Sure, Bayern, Barcelona and Real Madrid are all still in it. But no team left in the Champions League is historically dominant. Expected goals, a statistical measure of the quality of scoring chances a team creates and concedes, rates Barcelona as the top team in this year’s competition, but one with only a 28 percent change of winning the tournament.1All of the data in this article is current through April 10.This year’s Barcelona, however, does not make the top 10 list of expected goals difference for clubs since 2010-11. With fewer truly great teams in the mix, an upset winner is that much more likely. Here’s what to expect.Borussia Dortmund (60 percent chance of advancing) vs. Monaco (40 percent)With a position atop the Ligue 1 table, an impressive defeat of Manchester City in the round of 16, and an incredible 103 goals scored between Ligue 1 and the Champions League, Monaco might appear to have the resume of a quarterfinal favorite. However, Monaco’s numbers require some caution. Despite leading to 90 nonpenalty goals this season, the chances Monaco has created have been worth only about 58 expected goals (xG), according to the soccer stats-tracker Opta. Scoring 33 more goals than expected is unprecedented in the last few years. No other club has even beaten expected goals by 20 or more at this point in the season since 2010-11. While it is not terribly unusual for top teams to outperform their expected goals — top teams tend to have better finishers — Monaco is finishing chances better than any of Lionel Messi’s teams ever did.If Monaco’s goal scoring falls off, Dortmund should be well prepared to take advantage. Since returning from the winter break, Dortmund has been dominant, collecting 1.2 more xG per match than their opponents, compared with only a +0.7 margin before the break. With underlying numbers to match its goals difference and a recent spike in performance, Dortmund looks like the more likely semifinalist.In either case, this should be one of the most exciting matches of the round. Both Monaco and Dortmund depend on pace and quick-hitting attacks — both clubs lead their respective leagues in shot attempts following moves of two passes or fewer. While Thomas Tuchel may attempt to impose more control on the match than Pep Guardiola did against Monaco in the round of 16, the game is likely to be a fast-paced and attacking affair.Barcelona (65 percent) vs. Juventus (35 percent)This rematch of the 2015 Champions League final features the best attack-vs.-defense matchup of the round. This season Barcelona has created the second-most clear scoring chances (116), as defined by Opta, in the big five leagues, while Juventus has conceded the fewest clear scoring chances (20).Barcelona is well known for an attacking style that favors making the extra pass to create the highest-quality scoring chances, rather than trying to shoot the ball from far out. Juventus, under managers Max Allegri and Antonio Conte, has developed a defensive strategy that mirrors Barcelona’s attacking play. The Italian side focuses on defensive structure in order to prevent the same kinds of clear chances that Barca aims to create. A list of the best defensive seasons since 2010-11, judging teams by the number of quality chances they concede, shows Juventus dominating. And this year Juventus is preventing clear chances at its best rate ever, allowing only about one every other match.Barcelona was able to break through Juventus’ defense in the 2015 final just as Bayern Munich did during last year’s knockout stages. But in both of those cases, it took a top performance from one of the world’s best attacks to win the tie. Barcelona is rightly favored, but any slight drop-off in execution could see the Catalan side stymied by Juventus’ defense.Bayern Munich (71 percent) vs. Real Madrid (29 percent)ESPN’s Soccer Power Index rating gives a big boost to Bayern Munich based on the German side’s superior defensive numbers. Bayern has conceded just 23 goals in 36 matches between the Bundesliga and Champions League, while Real has conceded 43 in 38 matches. Some of this difference disappears when you look at expected goals, which drops Real’s total to 37. But it is not enough to erase it all.The two sides not only see different defensive outcomes, but they also play significantly different styles when out of possession. Carlo Ancelotti has his Bayern squad playing the high-pressing style preached by Pep Guardiola. When Bayern turns the ball over in midfield, it breaks up their opponents’ next possession within three passes about 55 percent of the time, the second-highest rate in the Bundesliga. Real Madrid, by contrast, defends much more passively, breaking up opposition possession in only about 45 percent of cases, 12th in La Liga.It is not that Real Madrid has been particularly poor defensively, but its more passive defensive style seems like a major risk against Bayern. Under manager Zinedine Zidane, Real Madrid has been an outlier among top clubs in not embracing the new, analytics-minded strategy of pressing on defense. It will be interesting to see if Real’s more old-fashioned defensive style can work. If Real fails to unsettle Bayern early in a possession, that would give time on the ball to central midfielders Arturo Vidal and Thiago Alcantara. That outcome would be risky at best for Real. Thiago in particular is having a great season, leading the Bundesliga with 96 progressive passes and runs. (These are defined as passes which advance the ball through midfield over 10 yards beyond where the possession had reached, or runs which progress similarly while eliminating a defender on the dribble.) Real Madrid may need to adjust its pressing rate to protect the defense from Bayern’s passers if it means to make it to another Champions League final.Atletico Madrid (75 percent) vs. Leicester City (25 percent)Leicester City presents something of a conundrum to any projection system, having won five of six league matches since sacking manager Claudio Ranieri. The club’s performances under new manager Craig Shakespeare have not been quite as good as its unbeaten record suggests — despite outscoring opponents in the league and CL by a combined 17-8, Leicester’s expected goals difference is just 10.3-9.1. But Leicester has produced more expected goals than its opponents in five of its seven matches after running negative in expected goal difference under Ranieri. It is certainly possible that Leicester will continue performing at this higher level under Shakespeare.However, it is hard to identify any key changes Shakespeare made. Leicester City remains the highest-tempo team in the Premier League, with more possessions per match than anyone else. The Foxes still work best without the ball, managing the same 42 percent possession rate as under Ranieri. What seems to have changed is not Leicester’s style of play, but the effectiveness of it. This is the sort of change, not linked to any obvious tactical shift, that analysts tend to be skeptical of. It might just be form, in which case the large SPI advantage to Atletico Madrid may be correct.For Atletico, this persistent Leicester style may present a problem. Atleti prefers to concede possession and play off the ball, especially against top opponents. But while Atletico is unusual in the Champions League for its roughly 50 percent possession rate, Leicester at 42 percent is more extreme. Atletico will likely need to adjust its typical knockout strategy and make use of ball possession to get past Leicester, even if the Foxes’ current run of form may not be entirely sustainable.Check out our club soccer predictions.