Guimaraes, signed for £75m from Newcastle on Saturday, was introduced at half-time at the Emirates Stadium after Myles Lewis-Skelly's opener had been cancelled out by Martin Baturina.
Lewis-Skelly's goal, stroked home after cutting out a poor pass from Como goalkeeper Jean Butez, came as he is linked with an Arsenal exit. He celebrated by making a heart gesture with his hands.
Guimaraes received a warm welcome from the home fans with his introduction but Arsenal were unable to find a second-half winner after Baturina showed impressive footwork then fired past Kepa Arrizabalaga for Como's leveller before half-time.
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Mikel Arteta left out Bukayo Saka, Declan Rice and Martin Zubimendi despite their returns from World Cup duty this week, but there were first cameos of pre-season from Eberechi Eze, David Raya, Mikel Merino and Noni Madueke.
The two sides played out a penalty shootout after the game, with Arsenal, who will face Manchester City at Wembley in the Community Shield on Sunday, winning 4-3 as new signing Christos Tzolis slammed home the decisive spot-kick.
More to follow...
