Chelsea, Manchester City under Champions League scrutiny
Unbeaten Chelsea faces Shakhtar Donetsk, which has won 12 straight in its league
Group D faces crunch time -- Manchester City at Ajax and Madrid at Dortmund
Milan boss Massimiliano Allegri is on the hot seat going against strong Malaga
Champions League action resumes Tuesday and Wednesday with Matchday Three. Here are five storylines to watch ...
1. European champion faces its toughest test. It's all hunky-dory at Stamford Bridge these days, with unbeaten Chelsea atop the Premier League table. We can no longer talk of it having coasted through a generous fixture list: it has now beaten Arsenal and Tottenham on the road and, while second-best for periods against Juventus (Matchday One, 2-2) and FC Nordsjaelland (Matchday Two, 4-0), is atop Group E going into a potentially tricky doubleheader against Shakhtar Donetsk.
The Ukrainian champion puts Chelsea's form to shame: 12 wins out of 12 in the league, while going back to last season it has won its last 21 matches and, in the last 12 months, picked up 79 points from a possible total of 81. Last summer Shakhtar rejected an offer from Zenit St Petersburg to buy Henrik Mkhitaryan, whose 17 goals in 19 matches this season have marked him out as a potential European star of the season. Will Chelsea's defense, fortified by the return of club captain John Terry, be able to withstand the pace, movement and dead-eye finishing of the clinical Armenian? Or will Roberto di Matteo's continued faith in "Ma-Zar-Car" -- the Juan Mata-Eden Hazard-Oscar attacking trident -- leave Shakhtar with a first home loss since November? With so much offensive talent, goals seem a certainty (so that will be 0-0, then).
2. Crunch time in Group D. Manchester City coach Roberto Mancini was an unhappy man even after Mario Balotelli netted his eighth consecutive penalty kick to secure an undeserved 1-1 draw at home to Borussia Dortmund on Matchday Two. This was the second successive European game in which City had been outplayed, and Mancini later spoke of "a problem" within the camp. He accused his players of not showing enough aggression, nor covering enough ground, against the excellent Germans.
With City off to Ajax and Dortmund hosting Madrid, the question is: can City be that bad for a third game running, and can Dortmund be that good? The Dortmund-Real game could be that matchup of this round, with a win putting either in the driving seat in the group. Last week also saw Real Madrid coach Jose Mourinho publicly back Cristano Ronaldo to win the Ballon D'Or. "It's impossible for Lionel Messi to win the award four times and Ronaldo only once," he said. Will those comments cure Ronaldo's famous "sadness?" We might find out on Wednesday.
3. Pellegrini eyes revenge, Milanese-style. Malaga coach Manuel Pellegrini's only season as Real Madrid coach, three years ago, started to come off the rails at exactly this point: Matchday Three in Champions League Group C, when AC Milan beat Madrid 3-2 at the Bernabeu, drew the return 1-1 and left the Spanish side, which had broken the bank on Kaka and Cristiano Ronaldo, with yet another Round of 16 failure.
Fast forward three years, and this time it's Milan boss Massimiliano Allegri under pressure: five defeats in eight league games, one point off the bottom of Serie A and every game billed as potentially his final one in charge. Wednesday's opponent, Malaga, has been a revelation of the group stage: the debutant has won its first two matches 3-0 and, in Spanish winger Isco, has one of the breakout stars of the campaign. Pellegrini is far too charming to admit it, but he might just enjoy getting his own back on the Rossoneri.
4. Is BATE Borisov the new Dynamo Kiev? There is a surprise name at the top of Group F: Belarussian champion BATE, which only came back into existence in 1996 after disbanding in 1981. Coached by former defender Viktor Goncharenko -- at 35 the youngest coach in the group stages and described as the "Belarussian [former Dynamo Kiev coach Valery] Lobanovsky" -- BATE has already beaten Lille and Bayern Munich (both 3-1) and this week faces Valencia, which represents its biggest threat to its first-ever qualification into the knockout phase.
"We are in a constant state of progress, whether that's our training base, stadium, squad, the development inside the team," Goncharenko told UEFA.com. "[Our success is down to] the constant hunger from the coaching staff for knowledge, plus the eagerness of the players." A place in the next round is within its grasp now.
5. Celtic can't do it again, can it? Fresh from its first away win in the Champions League after 20 attempts -- 3-2 at Spartak Moscow -- Scottish champion Celtic takes on Barcelona at Camp Nou on Tuesday, perhaps buoyed by the sight of the Catalans shipping four goals to Deportivo La Coruna in a crazy game Saturday. Barcelona has its worst defensive record in 10 seasons -- 11 conceded in eight league matches -- and last let in four back in March 2009, 218 games ago.
But that's as bad as it gets: the team remains unbeaten this season, coach Tito Vilanova has equaled the best-ever debut for a La Liga boss (with Sporting Gijon coach Diaz Novoa, 1979) while Lionel Messi, scorer of his 15th career hat trick at the weekend, now has eight goals in his last four matches. It was Mother's Day in Argentina on Sunday, hence newspaper Ole's front-page headline after the match: "Bless the Mother who gave birth to him!" Messi himself is set to become a father in the next few weeks, and it might be that Celtic's best hope of stopping him is if his partner, Antonella, goes into labor a bit early.