How to focus item in listbox from view model

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WPF

Caliburn.Micro

I make autocomplete and I want go throught with keys up and down in listbox with results. So I need change the focus from textbox to first listbox item.
For change the focus to listbox I used focusmanager. But focusmanager focus the listbox, not the first item. I have to press button down twice to start to walk throught the list. Changing property SelectedClient in listbox doesnt help.

What I have tried:

<TextBox Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2" Name="Client" Text="{Binding Client}" cal:Message.Attach="[Event KeyUp] = [Action ExecuteFilterView($executionContext)]" Validation.ErrorTemplate="{x:Null}" >
                    <TextBox.Style>
                        <Style>
                            <Style.Triggers>
                                <DataTrigger Binding="{Binding UserCanChooseClient}" Value="True">
                                    <Setter Property="FocusManager.FocusedElement" Value="{Binding ElementName=Clients}"/>
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </TextBox.Style>
                </TextBox>
<ListBox x:Name="Clients" Width="190" Height="auto" MaxHeight="400" Margin="5 28 0 0" cal:Message.Attach="[Event KeyUp] = [Action ExecuteClientsView($executionContext)]; [Event MouseLeftButtonUp]=[Action HandleClientChosenClick($eventArgs)]" ScrollViewer.HorizontalScrollBarVisibility="Hidden" ScrollViewer.VerticalScrollBarVisibility="Hidden" SelectedItem="{Binding Path=SelectedClient}" ItemsSource="{Binding Path=Clients}" DisplayMemberPath="Description" SelectedValuePath="Code"></ListBox>