While 1.a3! is a useful choice of opening against over-booked juniors, it has the slight drawback of giving black too free a hand in reply. If you are reasonably confident your opponent will meet 1.e4 with e5 then you have the chance to try Mengarini's Opening instead.
It starts off as a Vienna, with 1.e4 e5 2.Nc3 Nf6 (in my experience 2.Nc3 is always met with 2. ... Nf6) and only now do you play 3.a3! (For maximum effect, gently slide the pawn with the pinky of your left hand). While you have essentially handed the White pieces to your opponent, you have managed to rule out a number of opening choices for him/her, including the Ruy Lopez.
One tricky line for White is if Black continues with 3. ... d5 The you can enter a favourable line of the Scotch (reversed) with 4.exd Nxd5 5.Qh5! as 5. ... Nb4 is not available to Black.
Of course Black may instead try and cross your plans by choosing something different, or in the game below, chickening out entirely with an early a6. If your opponent does decide to give the White pieces back, chalk it up as a moral victory, and convert your mental advantage into a material one.
Press,Shaun - Telfer,Ken [C47]
Tuggeranong v Woden, 1989
1.e4 e5 2.Nc3 Nf6 3.a3 Nc6 4.Nf3 a6 5.d4 d6 6.dxe5 dxe5 7.Qxd8+ Kxd8 8.Bg5 Be6 9.0-0-0+ Kc8 10.Bh4 h6 11.Bg3 Bd6 12.Nd2 b5 13.f3 Nd4 14.Bd3 c5 15.Ne2 Nc6 16.c3 Nd7 17.Nf1 Kc7 18.Ne3 Ne7 19.Rd2 f6 20.Rhd1 Nc8 21.Bf2 c4 22.Bc2 Ndb6 23.Ng3 Rd8 24.Nef5 Rd7 25.Bxb6+ 1-0