Cap was fast. Not necessarily [i]faster[/i] than the Winter Soldier, but ... she wasn't slower either. Her warning fell on deaf ears, the Winter Soldier couldn't be threatened, he was programmed to ignore fear, desensitised to it so much so that he wasn't capable of feeling fear even as he faced almost certain death. For a moment, before the fight erupted into action, the Winter Soldier and Captain America stood face to face, sizing one another up, playing a psychological game, trying to intimidate the other, instil fear, but neither side crumbled under the pressure. 

Cap's flying kick was fast, and powerful, not quite fast enough though, Winter Soldier's synthetic arm was just a fraction faster. The kick didn't connect with his chest as it should have, instead it was knocked somewhat off course by his star-emblazoned arm, combat knife primed and ready in the other hand, the blow to his arm was enough to stagger him back a half step though, but neither combatant was floored by the attack and defence manoeuvres. 

The Winter Soldier knew that Karpov's orders were explicitly "Kill Captain America", Haines was not important, she was perishable, whether she lived or died was irrelevant, same with all the other SHIELD agents down below. Despite Kapov's instruction to ignore the captive, The Winter Soldier knew she was a valuable obstacle in Captain America's path. The Soldier needed to prevent her escape. Haines inched toward the door, exhausted and overwhelmed from her experience, she could barely stand, but she wasn't too large or heavy, the SHIELD agents could shuffle her out relatively easily. 

The Soldier grappled with Captain America, attempting to haul her over the upper railings down to the concrete warehouse floor below, to cut off the SHIELD agents escape and keep Haines thoroughly in the way. Captain America was nothing like Haines though, she could fight, she was tough, and she didn't budge easily. Seconds of the struggle ticked by and Haines was ever closer to slipping away. At the very least, if The Winter Soldier lost Haines, there were still a handful of SHIELD agents the would make useful human shields to get in Captain America's way.