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The England winger has been pleading for the central striker's role for some time and, playing in his new position, Walcott proved he has what it takes to fill the boots of the London club's all-time top scorer Henry.
"He can play through the middle, I am convinced of that," manager Arsene Wenger told the club's website after his team climbed to fifth in the table, 16 points behind leaders Manchester United.
"He can only get stronger in there. He has done very well and it just typifies what I think he can do."
Walcott was on target in the 20th and 73rd minutes before adding his third goal in stoppage time.
Olivier Giroud (2), Alex Oxlade-Chamberlain and Lukas Podolski also struck for Arsenal while two-goal Demba Ba and Sylvain Marveaux replied for Newcastle.