Danny Welbeck registered a hat trick as Arsenal got their Champions League campaign up and running last night with a 4-1 victory at home to Galatasaray.

The London side were ruthless as they collected their first points of this season's Champions League group stage and were only stopped in their tracks when travelling supporters threw flares on to the Emirates pitch.

Even then the delay was only temporary. With England manager Roy Hodgson looking on from the stands, Welbeck - a £16m deadline-day signing from Manchester United - produced a clinical display to mark Arsene Wenger's 18th anniversary as manager with a comprehensive win.

However, UEFA are likely to launch an investigation into the unsavoury scenes 20 minutes into the match in which play halted after several flares were thrown from the away end, with Galatasaray goalkeeper Fernando Muslera and captain Wesley Sneijder helping restore calm as riot police surrounded the Galatasaray fans. There had been several arrests made outside the stadium already, after a band of supporters tossed flares into a pub.

There was agitation among the players too, as the Turkish side fell behind just 22 minutes into the game when Welbeck steered a delectable pass from Alexis Sanchez into the net. The Arsenal striker then doubled his tally eight minutes later with another neat finish, galloping on to a back-header to score.

Sanchez - who had earlier been felled by a two-footed lunge from defender Felipe Melo, a tackle which was only punished by a yellow card - slid a third goal past goalkeeper Fernando Muslera just before the break. Welbeck duly completed the first competitive hat trick of his career after 52 minutes.

The night was blotted for the hosts when goalkeeper Wojciech Szczesny clattered Burak Yilmaz to incur a red card and concede a penalty. The Galatasaray striker then converted from the spot to provoke some consternation among the home support, albeit they were later appeased by the sight of substitute goalkeeper David Ospina making a number of smart saves during the closing stages. Perhaps his best stop came when he clawed away a shot from substitute Hamit Altintop with just eight minutes left.

Arsenal now face Barclays Premier League leaders Chelsea on Sunday in confident mood. The composure that was shown by Welbeck in front of goal was an obvious positive for Wenger, while the Frenchman will reflect too that Sanchez and Mesut Oezil combined well on the left flank, with Santi Cazorla and Alex Oxlade-Chamberlain providing a further, consistent threat.

The Arsenal defence was tested by the red card shown to Szczesny and the counter-attacking power of their Turkish visitors but remained resolute. Telles Alex sent the ball spinning wide of a post and Ospina was required to deflect a series of shots later in the second half, yet the home side remained strong.

This will be a point of satisfaction for Wenger, not least since his players had toiled so badly in their opening group match away to Borussia Dortmund. In Germany, Welbeck had been wasteful and Oezil, among others, laboured and unsure in attack. But here was a confident Arsenal, a team capable of winning and ruthless when given chances to prove it. The result has allowed the London side to move into second spot in Group D, with Galatasaray now at the bottom.