Rather than take the long way around to find the sword and then beat the door guard, go down and right from your starting position, wait for the guard to approach, then run left just before he is within striking range. You should be able to lure him with you into the next room. Run all the way left and climb up just before he comes within range again. Go left, probe the ceiling in the next room for a hidden passage, go up and then right again to return to the starting room. From here, go down (you'll end up to the right of the guard), and quickly dash right toward the exit. You'll be able to finish the level without ever fighting the guard, and from level 2 onwards you'll automatically be given the sword even though you never collected it.