The 2013/14 season UEFA Champions League group stage opening round of matches that kicked off this week highlighted teams that are ambitious, and carry the favourites tag.But the games also revealed the underdogs, who are merely making up the numbers.Some of the big guns started on a winning note, while a few suffered shock defeats.Reigning champions Bayern Munich, Real Madrid, Barcelona, Manchester United, Manchester City, Paris St-Germain, Napoli, AC Milan, Schalke04, Atletico Madrid and Arsenal all recorded comfortable wins.Chelsea and Juventus are among top teams that suffered early set-backs.Juventus were held by FC Copenhagen of Denmark, while the 2012 champions Chelsea lost to FC Basel at Stanford Bridge.Juve were drawn alongside Real Madrid, FC Copenhagen, and Galatasary.Drawing their opening game against the underdog side in the group means the Italian champions would have to collect as many points as possible from the remaining matches if they are to overhaul Real Madrid from top spot.The second position is always dangerous as teams are always seeded against stronger opponents in the knock-out phase.This usually prompts early exit, accumulation of yellow cards or even injuries to key players due to early pressure in the competition.After failing in two successive seasons, Manchester City managed to register a comfortable win in the Champions League.They now seem well positioned to progress from the group stage alongside Bayern Munich.However, Arsenal, despite winning away at French side Olympique Marseille, face a tough huddle to qualify from the group that also has the likes of Napoli and last year’s losing finalists Borrussia Dortmund.Arsenal lack strength in depth and their squad are now only one or two injuries to be exposed to the bone. With the current fixture congestion, the Gunners are likely to suffer problems related to injuries and fatigue.Both Napoli and Dortmund are very strong teams with skillful players in their squad. They have players who can frustrate Arsenal’s offensive game.In this group, Marseille seem to be the underdogs and will find it had to collect even five points in total.Rafa Benitez has started off his reign at Italian side Napoli, who made a bright start to the competition by beating Dortmund in Naples, and now face Arsenal next week in England, which the Spanish manager calls his second home after spells with English sides Liverpool and Chelsea.In this group, only Benitez has won the Champions League (during his time at Liverpool) and will use his vast experience to guide the in-form Napoli to the knockout stage.The likes of Bayern, Barcelona, PSG and Real Madrid have already underlined their strong ambitions and one of them could be the eventual champions come May 2014.Spanish giants were the biggest winners on the opening round of matches. Real Madrid walloped Galatasary of Turkey 6-1 with Cristiano Ronaldo helping himself to a hat trick, and a day later Barca beat Ajax 4-0 with a hat trick from four-time world player of the year Lionel Messi.Champions League reigning champions Bayern of Germany comfortably beat Russian champions SKA Moscow 3-0.Pep Guardiola seem to have changed the Bavaria attacking system as they now attack from the middle other than using the wings as was the case under former coach Jupp Heyckes.If Bayern can resort to their natural attacking style they will score more goals than they will concede and will become a very difficult side to beat.It looks they have a real chance to become the first team to successfully defend their Champions League title.