Bayern Munich's Kingsley Coman in action before scoring their first goal. (Reuters Photo) LONDON, November 1 (Reuters): Kingsley Coman and Javi Martinez fired Bayern Munich into the knockout stages of the Champions League, netting a goal each as they beat Celtic 2-1 in their Group B clash on Tuesday to make it two wins out of two against the Scottish champions. The victory puts the German side on nine points after four games, three behind leaders Paris Saint Germain and six ahead of third-placed Celtic, and their superior record against the Scots guarantees them a top-two spot in the group. Though the hosts started well, Coman broke the deadlock for Bayern in controversial fashion in the 22nd minute, appearing to handle a long ball from goalkeeper Sven Ulreich before firing home following a horrendous mix-up in the Celtic defence. After creating the goal, Ulreich had to come to his side's rescue early in the second half, getting down smartly to steer Stuart Armstrong's shot behind for a corner. Callum McGregor put Celtic back on level terms in the 74th minute, latching on to James Forrest's clever pass before sliding the ball between Ulreich's legs. The lead lasted only three minutes as Martinez headed Bayern back in front, sustaining a nasty cut above his eye in a clash of heads with Celtic defender Nir Bitton in the process. Celtic shifted to a three-man backline as they chased another equaliser but even with six minutes of time added due to the injuries to Martinez and Bitton, the Hoops could not fashion an equaliser. In the other game in Group B PSG hammered bottom side Anderlecht 5-0 to make it four wins in four games for the French champions. Barca held by Olympiakos Barcelona must to wait to confirm a place in the Champions League last 16 after dropping points for the first time in Group D in an absorbing 0-0 draw at Olympiakos Piraeus on Tuesday. On his return to his former club, Barca coach Ernesto Valverde watched his in-form side dominate for long spells and create some great chances, but the determined home team held on for their first point as they bid for a Europa League spot. Olympiakos goalkeeper Silvio Proto was a prominent figure in a frenetic and surprisingly open match at the Georgios Karaiskakis stadium, coming to the rescue to deny Lionel Messi and Luis Suarez on several occasions. Barcelona top the section with 10 points, having extended their unbeaten run in all competitions to 15 matches with 13 wins and two draws, ahead of Juventus on seven points after their 1-1 draw at Sporting who have four. Takis Lemonis' Olympiakos team, who are also struggling in the Greek SuperLeague, finally opened their account as Barca were held to a goalless draw for the first time since April. Valverde, who won three league titles as Olympiakos coach in two spells at the Piraeus club between 2008 and 2012, was given a rousing welcome by the home fans who held up a giant banner which read “Ernesto thanks for everything”. “I was very moved by the whole experience of coming back here tonight,” said Valverde. “I love the fans here and they appreciate my work; it was amazing to see such a reception for an opposing coach – it speaks volumes for them really.” “Olympiakos is a very strong team and with the help of their fans they have achieved a great result and we congratulate them for that. I would love to see them qualify to the next stage but there is a long way to go yet.” United close in after beating Benfica Manchester United are almost certain to reach the knockout stage of the Champions League after they beat Benfica 2-0 at Old Trafford on Tuesday to make it a perfect four wins in Group A. An own goal by Benfica's 18-year-old keeper Mile Svilar on the stroke of halftime and a Daley Blind penalty in the 78th minute were enough for United, who struggled at times to find their fluency. Jose Mourinho's team now need just a point from their final two games in the group, against Basel and CSKA Moscow, to make absolutely certain of their place in the knockout stage for the first time in four years. The result moved them six points clear at the top of the group, yet United, who qualified by winning the Europa League last season, were well below their best, labouring in midfield and sloppy at times at the back.