diff --git a/CHANGELOG.md b/CHANGELOG.md
index a1324948a..144e36d57 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Fix missing session when trying to display an error duing bookmarking. (#1984)
 
+* Fixed `set()` method of `InputSelectize` controller so it clears existing selections before applying new values. (#2024)
+
 
 ## [1.4.0] - 2025-04-08
 
diff --git a/shiny/playwright/controller/_input_controls.py b/shiny/playwright/controller/_input_controls.py
index a3fde3dfa..de95c6dd0 100644
--- a/shiny/playwright/controller/_input_controls.py
+++ b/shiny/playwright/controller/_input_controls.py
@@ -1187,21 +1187,71 @@ def set(
         """
         Sets the selected option(s) of the input selectize.
 
+        Selected items are altered as follows:
+        1. Click on the selectize input to open the dropdown.
+        2. Starting from the first selected item, each position in the currently selected list should match `selected`. If the item is not a match, remove it and try again.
+        3. Add any remaining items in `selected` that are not currently selected by clicking on them in the dropdown.
+        4. Press the `"Escape"` key to close the dropdown.
+
         Parameters
         ----------
         selected
-            The value(s) of the selected option(s).
+            The [ordered] value(s) of the selected option(s).
         timeout
             The maximum time to wait for the selection to be set. Defaults to `None`.
         """
         if isinstance(selected, str):
             selected = [selected]
+        # Open the dropdown
         self._loc_events.click()
-        for value in selected:
-            self._loc_selectize.locator(f"[data-value='{value}']").click(
-                timeout=timeout
-            )
+
+        # Sift through the selected items
+        # From left to right, we will remove ordered items that are not in the ordered `selected`
+        # If any selected items are not in the current selection, we will add them at the end
+        i = 0
+        while i < self._loc_events.locator("> .item").count():
+            item_loc = self._loc_events.locator("> .item").nth(i)
+            item_data_value = item_loc.get_attribute("data-value")
+
+            def delete_item(item_loc: Locator) -> None:
+                """
+                Deletes the item by clicking on it and pressing the Delete key.
+                """
+                item_loc.click()
+                self.page.keyboard.press("Delete")
+
+            # If the item has no data-value, remove it
+            if item_data_value is None:
+                delete_item(item_loc)
+                continue
+
+            # If there are more items than selected, we need to remove the extra ones
+            if i >= len(selected):
+                delete_item(item_loc)
+                continue
+
+            selected_data_value = selected[i]
+
+            # If the item is not the next `selected` value, remove it
+            if item_data_value != selected_data_value:
+                delete_item(item_loc)
+                continue
+
+            # The item is the next `selected` value
+            # Increment the index!
+            i += 1
+
+        # Add the remaining items
+        if i < len(selected):
+            for data_value in selected[i:]:
+                # Click on the item in the dropdown to select it
+                self._loc_selectize.locator(f"[data-value='{data_value}']").click(
+                    timeout=timeout
+                )
+
+        # Close the dropdown
         self._loc_events.press("Escape")
+        return
 
     def expect_choices(
         self,
diff --git a/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/app_selectize.py b/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/app_selectize.py
new file mode 100644
index 000000000..ed9fb0ff5
--- /dev/null
+++ b/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/app_selectize.py
@@ -0,0 +1,21 @@
+from shiny import App, render, ui
+from shiny.session import Inputs, Outputs, Session
+
+app_ui = ui.page_fluid(
+    ui.input_selectize(
+        "test_selectize",
+        "Select",
+        ["Choice 1", "Choice 2", "Choice 3", "Choice 4"],
+        multiple=True,
+    ),
+    ui.output_text("test_selectize_output"),
+)
+
+
+def server(input: Inputs, output: Outputs, session: Session) -> None:
+    @render.text
+    def test_selectize_output():
+        return f"Selected: {', '.join(input.test_selectize())}"
+
+
+app = App(app_ui, server)
diff --git a/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/test_app_selectize.py b/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/test_app_selectize.py
new file mode 100644
index 000000000..e09cc9323
--- /dev/null
+++ b/tests/playwright/shiny/bugs/2013-selectize-set-does-not-clear/test_app_selectize.py
@@ -0,0 +1,29 @@
+from playwright.sync_api import Page
+
+from shiny.playwright import controller
+from shiny.pytest import create_app_fixture
+from shiny.run import ShinyAppProc
+
+app = create_app_fixture("app_selectize.py")
+
+
+def test_inputselectize(page: Page, app: ShinyAppProc):
+    page.goto(app.url)
+
+    input_selectize = controller.InputSelectize(page, "test_selectize")
+    output_text = controller.OutputText(page, "test_selectize_output")
+
+    input_selectize.set(["Choice 1", "Choice 2", "Choice 3"])
+    output_text.expect_value("Selected: Choice 1, Choice 2, Choice 3")
+    input_selectize.set(["Choice 2", "Choice 3"])
+    output_text.expect_value("Selected: Choice 2, Choice 3")
+    input_selectize.set(["Choice 2"])
+    output_text.expect_value("Selected: Choice 2")
+    input_selectize.set(["Choice 2", "Choice 3"])
+    output_text.expect_value("Selected: Choice 2, Choice 3")
+    input_selectize.set(["Choice 1", "Choice 2"])
+    output_text.expect_value("Selected: Choice 1, Choice 2")
+    input_selectize.set([])
+    output_text.expect_value("Selected: ")
+    input_selectize.set(["Choice 1", "Choice 3"])
+    output_text.expect_value("Selected: Choice 1, Choice 3")