You can use key bindings to create custom shortcuts. show Completions show Completion (ok)

https://forum.sublimetext.com/t/customize-shortcuts/7566/3

You can use key bindings to create custom shortcuts.
To create keybindings in the key map file, go to

[On Windows] Preferences > Key Bindings - User
[On OS X] Sublime Text > Preferences > Key Bindings - User

I have written complete tutorial on creating custom keyboard shortcuts in Sublime Text

[
 { "keys": ["ctrl+space"], "command": "auto_complete" },
 { "keys": ["ctrl+space"], "command": "replace_completion_with_auto_complete", "context":
    [
      { "key": "last_command", "operator": "equal", "operand": "insert_best_completion" },
      { "key": "auto_complete_visible", "operator": "equal", "operand": false },
      { "key": "setting.tab_completion", "operator": "equal", "operand": true }
    ]
  }
]