How to use Q.denodeify while converting Node async functions to promises?

Following code works just fine:

var Q = require('q');

function async_f1(callback) {
    var deferred = Q.defer();
    setTimeout(function() {
        deferred.resolve("Async function 1...");
    }, 1000);
    return deferred.promise;
}

function async_f2(callback) {
    var deferred = Q.defer();
    setTimeout(function() {
        deferred.resolve("Async function 2!...");
    }, 1000);
    return deferred.promise;
}

function async_f3(callback) {
    var deferred = Q.defer();
    setTimeout(function() {
        deferred.resolve("Second async function 3!...");
    }, 1000);
    return deferred.promise;
}

Q.spread([async_f1(), async_f2(), async_f3()], function(a, b, c) {
    console.log(a, b, c);
})

But I really don't think it's the best way to convert async functions into promises. There are a lot of repeatings of defer stuff. I've read some about Q.denodeify feature but I was unable to implement it.

Could you show me how it is done in this particular case?

Thank you