Combat is Visceral, make them feel it.

Try this once.
Don't track hit points.
Every time a player character is hit by an attack  describe the wound the player takes.
Tell them some negative effect it has.

• You took a wound to your sword arm you have to switch to your off hand, what do you do?
• You took that wound to your leg your movement is halved, you're bleeding, what do you do? 
• That blow hit your back pack, you can hear a potion bottle or oil flask shatter, what do you do?
• You shield has cracked what do you do?
  
• You have been disarmed what do you do?
• The left most shoulder strap on your chest plate has been severed. It's hanging limp and  impeding your  actions, your going to have to refasten it to loose the chest plate, what do you do?
• You take a stiff blow to the  chest knocking the wind out of you, what do you do?
• A minor cut to the cheek, that's going to leave a mark, what do you do?
• The enemy has caught i't weapon in your cloak tangling the two of you momentarily, what do you do?
• The enemy has brushed aside your guard leaving you open for attack, what do you do?
• The  sundering blow smashes the radius of your  shield arm, it now hangs limp at your side, what do you do.
• Your lip is busted open, teeth go flying, what to you do?
• Spear to the hip, blood everywhere, What do you do.
• Your armor turns the blade, but  the impact may have broken your collar bone, what do you do?

I'm sure you can come up with about a hundred more effects that are better than the examples above.

Always ask the  player after he gets hit "what do you do" if if they stall the monster attacks again.
Tell them up front that this is going to happen, apply the rule evenly, openly, and fairly. If you want to use a 20 second stop watch, use one.

For each hit on a player character, access a minus -1 to the player characters to hit rolls.

When the Player character can no longer mathematically hit the target then the next successful attack accessed against the character is the death blow.

Healing  and long rest remove these penalties and injuries. (By long rest I mean  real recovery times, if the characters radius breaks, a nice night in the inn is not going to do it, they need a few weeks and honestly may never be quite the same again, or they need a priest with cure moderate wounds.... or your games equivalent.)

Do the same when a character hits a monster do not worry about rolling damage. Describe HOW the hit landed, and WHAT effect the hit has.

• Be as descriptive and visceral as possible.
• Throw away  any critical hit or fumble  rules.
• Feel free to give characters and Monsters second free attacks when it fits. 
• Run this as fast as possible.

Monsters die after a any number of hits, it's the GM's discretion. (I would suggest keeping it at around  5 or under.) *EDIT: Or one hit per Hit Die.

In the end  want my players to be out of breath and sweating after the fight.

I want them to think twice about fighting again.

Never forget that every damn time that character draws steal or starts to cast a spell, someone is going to die, it's a fight, a real fight.
The characters are RISKING THEIR LIVES, THEIR HEALTH, AND THEIR FUTURES.
Make them feel it.

-Thanks for reading
Mark.